A LABORATORY OUTLINE OF GENERAL CHEMISTRY GENERAL CHEMISTRY A CULTURAL COURSE BASED UPON THE TEXT- BOOKS OF THE LATE ALEXANDER SMITH BY JAMES KENDALL, F.R.S. 676 pp. With lU illustrations and 170 cuts. NEW YORK, THE CENTURY CO. A LABORATORY OUTLINE OF GENERAL CHEMISTRY AN EXPERIMENTAL COURSE BASED UPON THE MANUALS OF THE LATE ALEXANDER SMITH By JAMES KENDALL, F.R.S. PROFESSOR OF CHEMISTRY, UNIVERSITY OF EDINBURGH FORMERLY PROFESSOR OF CHEMISTRY AT COLUMBIA UNIVERSITY AND AT NEW YORK UNIVERSITY NEW YORK THE CENTURY CO. Copyright, 1927, by THE CENTURY CO. 298 PRINTED IN U. 8. A. PREFACE This Laboratory Outline has been arranged to parallel, by simple and suggestive experiments, the subject matter presented in Smith-Kendall's General Chemistry. The directions for each experiment are given in sufficient detail to enable the book to be used by students who are taking chemistry for the first time. It is understood that no class will find it possible to perform all the experiments contained in the Outline. The interests of the teacher, the sex of the pupils, the local industries, and other factors will assist to determine the placing of greater emphasis on some experiments and the exclusion of others. All modern laboratory manuals contain quantitative experi- ments. If the laboratorj^ in which the students using this outline are accommodated lacks the simple balances, or the burettes, which quantitative work requires, these experiments must be omitted. In such cases, however, the teacher should discuss in detail, in the class-room, data such as these experiments would yield, and show how the conclusions demanded in the Outline can be reached. Every effort must be made to prevent the mere mechanical performance of the directions given, without thought about the chemical principles involved. The questions asked in the Outline are intended to call attention to the chemical significance of the w^ork. The experiment will teach nothing, unless the pupil is required to answer these questions in his or her laboratory notes. The exact method to be followed by the class in recording the results of laboratory work is, of course, a matter which is best left to the discretion of the individual instructor. The large size of laboratory sections in most colleges at the present time, however, necessitates that the time spent by assistants in the correction of laboratory records be reduced to a minimum. The plan described in Note 1 of the General Instructions at the beginning of the Outline is consequentl}^ recommended to the attention of instruc- tors, since it has been found by personal experience to be one which V VI PREFACE is both economical and efficient. The increase in page size of this volume over that of preceding laboratory manuals in the Alexander Smith series is expressly intended to facilitate the employment of this plan. The chief objection that may be raised against it — namely, that the student should acquire experience in writing connected statements of his laborator}^ work — may be met b}' assigning Home-Study Questions upon the more important and involved points of each exercise, as suggested in the General Chem- istry (pp. 9-10). Before starting work in the la})oratory, the class should Ix' instructed to read carefully the Hints in Connection with Labora- tory Work given on pp. 6-8 of the General Chemistry. At the end of each week the class should be examined and the experiments that have been performed should be discussed in the class-ropm. The teacher may thus make certain that the object of each exer- cise has been fully appreciated and that the significance of the results obtained has been clearly understood. In the course of this discussion, particular emphasis should be placed upon the practical applications of many of the experiments. vrs Kexdall. CONTENTS exercise page 1. Study of Bunsen Burner 1 2. Substances and Properties 2 3. Glass-working. Simple Bends 4 4. Construction of a Wash-Bottle 6 5. Capacities of Vessels. Weighing and Density 8 6. Density Determinations and Experimental Errors 10 7. Changes in Metals Heated in Air 14 8. Mixtures and Compounds 16 9. Composition and Formula of Nickel Sulphide 19 10. Composition and Formula of an Oxide of a Metal 21 11. Oxygen, Preliminary 23 12. Oxygen. Preparation and Properties 24 13. Weight of a Liter of Oxygen 27 14. Hydrogen. Preliminary 30 15. Hydrogen. Preparation and Properties 33 16. Valence of a Metal by Displacement 35 17. Water. Physical Properties 38 18. Hydrates 40 19. Quantitative Measurement of Water of Hydration 42 20. Atomic and Molecular Weights 44 21. Solvents and Solubility 45 22. Solubility and Temperature. Saturation 47 23. Hydrogen Chloride. Preparation and Properties 48 24. SoDiiLvi Hydroxide 51 25. Chlorine. Preparation and Properties 53 26. Chemical Equilibrium 55 27. Displacement 57 28. Double Decomposition 58 29. Ionization of Acids, Bases and Salts 59 30. Acids and Bases. Neutralization 62 31. Titration 64 32. Bromine 67 33. Iodine 69 34. Comparison of Hydrogen Halides 71 35. Hydrogen Peroxide 73 36. Bleaching Powder 75 37. Chlorates 76 38. Sulphur 78 vii VIU CONTENTS EXERCISE PAGE 39. Hydrogen Sulphide 80 40. Hydrolysis 82 41. Sulphur Dioxide 83 42. Sulphuric Acid 85 43. Nitrogen from the Air 87 44. Carbon Dioxide in Air and in the Breath 89 45. Ammonia 90 46. Hydroxide and Salts of Ammoniuai 92 47. Nitric Acid 94 48. Nitric Oxide 96 49. Nitrous Oxide 98 60. Phosphine and Phosphoric Acid 100 51. Arsenic Trioxide 101 52. Carbon 102 53. Carbon Dioxide 104 54. Carbon Monoxide 106 55. Methane and Acetylene 109 56. Starch and Sugars Ill 67. Acid and Alkaline Soils 1 13 58. Fertilizers 114 59. Fermentation 116 60. Acetic Acid 118 61. Destructive Distillation of Wood and Coal 119 62. Wood Charcoal and Bone Black 121 63. Tests for Food Components 123 64. Food Components of Milk 124 65. Food Components of Flour 125 66. Esters. Soap 126 67. How Soap Cleanses 128 68. Colloidal Suspensions 129 69. Dyeing. Dyes and Perfumes 131 70. Recognition of Substances 1 133 71. Recognition of Substances II . . .^ 136 72. Sodium Bicarbonate. Acid Salts 138 73. Potassium Nitrate 140 74. Calcitbi Oxide and Hydroxide 142 75. Hard Water ,^ 143 76. Flame Tests for Metals 144 77. Compounds of Magnesium 145 78. Aluminium Hydroxide. ALirNi 146 79. Analysis of Baking Powder 147 80. Reactions of Iron Compounds 149 81. Separation of Lead, Mercury and Silver 152 CONTENTS IX exercise page 82. Displacement of Metals. Couples 154 83. Identification of Metals in Group II 156 84. Identification of Metals in Group III 159 85. Identification of Metals in Groups IV and V 160 86. Recognition of Substances III 161 87. Analysis of a Coin 163 Appendix 165 GENERAL INSTRUCTIONS Read the " Regulations " posted in the laboratory. Read also, attentively, the following notes : Note 1. — Each student must secure a supply of loose-leaf note paper in ruled sheets approximately 9 inches long and 5 inches wide, upon which a concise record of all observations and deductions re- sulting from his experimental work is to be made. Upon the top of each sheet the student's name and desk number, with the name of his laboratory assistant and any other necessary information, are first written. The remainder of the sheet is then fitted into the Outline over the blank interleaf opposite the directions to the ex- ercise which is being performed, and a piece of carbon paper is inserted between the loose sheet and the blank page. The answers to all specific questions in the text, all observations and conclusions therefrom, together with the results of weighings, etc., in quanti- tative experiments, are written down immediately (also, of course, legibly) on the loose sheet as the student proceeds through the experiment. Only the briefest remarks are called for, and no attempt, should be made to work up a continuous narrative or to enter into any detailed discussion. At the end of the laboratory period, the loose-leaf copy of the student's notes is handed to his assistant for inspection and correction, the duplicate record on the interleaf being retained for his own use. (See also the Preface to this Outline, p. v, and General Chemistry, pp. 6-10.) Note 2. — Whenever an interrogation point or a direct ques- tion appears, a corresponding observation or answer should ap- pear in the student's notes. The "(?)" indicates something to be observed and recorded. Note 3. — The very numerous questions asked in the course of this outline are intended to be answered, not by speculation, but by careful observation and reasoning based on the results of this. Very often the student will find it necessary to devise and carry out further experiments of his own before a satisfactory answer is obtained. When a question occurs to you, endeavor by xi Xll GENERAL INSTRUCTIONS reflection and study to answer it yourself before consulting an in- structor. Note 4. — In many cases the work outlined could not in itself furnish the basis for an answer, and fuller investigation of the point would require work beyond the time or ability at the dis- posal of the beginner. Such questions are distinguished by refer- ences to Smith-Kendall's General Chemistry, the page where the necessary information may be obtained being indicated in bold type between square brackets. This text should be consulted, however, only after the experiments have been made and the notes written up as far as possible. Cross-references to other experi- ments in this laboratory outline are also frequently given. Note 5. — When a chemical change has been observed the equation should always be given in the notes, but an equation alone is seldom a sufficient record. .Note 6. — Where the word [Instructions] appears, consult the instructor before going further. Note 7. — In quantitative experiments, marked [Quant.], use the finer balance ; in all other cases the rough scales in the laboratory. Note 8. — The expression [Storeroom] indicates that the neces- sary apparatus is not included in the individual outfits. Note 9. — When the word [HOOD] appears, the operation is not to be conducted in the open laboratory. The apparatus is to be placed at once close to the desk-ventilator, or transferred to the hood. Note 10. — Where exact quantities are not indicated, very small amounts of solutions (1 c.c. or less) should be taken. This advice is given, partly to secure sa\*Jng of material, but chiefly to avoid the waste of time which working with large quantities always entails. Note 11. — To obtain the necessary chemical substances, if the chemicals are not fiitnishcd in '' kits " to each student, do not carry the bottles from the side-shelf to the desk. Bring a clean test-tube for liquids and a watch-glass for solids. For the latter, a piece of paper, provided near the side-shelf, may also be used. When too much of any reagent has been taken, do not return it to the bottle. GENERAL INSTRUCTIONS XUl Note 12. — The chemicals, if on a side-shelf, are divided into two sets, each arranged alphabetically according to the scientific names. The first set consists of solids in small bottles, the second of liquids. The bottles and their places are numbered consecu- tively to facilitate accurate replacement, and scrupulous care must be taken not to disarrange them. Read the labels atten- tively, as there are frequently several kinds of the same substance {e.g., pure, commercial, dilute, concentrated, and normal). All materials are supplied through the storeroom service. Do not therefore take side-shelf bottles, when found empty, to the instructor, but to the storekeeper for refilling. Note 13. — The expression [From Instructor], however, indi- cates one of a few special substances for which the student must apply to an instructor. Note 14. — The bottles on the desk, if there are any, contain certain substances which are frequently used. These substances will not be found on the side-shelf. Note 15. — When any acid gets upon the clothing, apply ammonium hydroxide solution at once. Note 16. — Burns, whether caused by contact with hot objects, by acids, or by corrosive liquids like bromine, are rubbed gently with a paste of sodium-hydrogen carbonate and water. All burns, save the slightest, must afterwards be dressed with an aqueous solution of boric acid (half-saturated) to prevent in- fection. Obtain the assistance of an instructor. Cuts must be washed in running water and dressed with boric acid as above, or with lanolin containing 2 per cent of boric acid. Note 17. — All students work independently, except where cooperation is expressly directed. A LABORATORY OUTLINE OF GENERAL CHEMISTRY EXERCISE 1 Study of Bunsen Burner Object: To learn how to use a Bunsen burner. Apparatus: Bunsen burner. Rubber tubing. Evaporating dish. a. Attach the Bunsen burner by means of rubber tubing to a gas connection, close the air-holes at the base, and light. In Ughting a Bunsen burner, turn on the gas first, and then bring a lighted match over the tube of the burner (?). Now open the air-holes gradually and note the effect upon the flame (?). Some- times the flame descends and burns noisily at the bottom of the tube. This back-fire happens when too much air is admitted. Shut off the gas, close the air-holes, turn the gas on again, and relight. b. Close the air-holes again, and hold a porcelain dish in the flame. What is deposited on the dish? When using the burner for heating purposes, always regulate the air supply so as to get a noiseless, non-luminous flame. c. Unscrew the tube of the Bunsen burner, turn on the gas, and light it (?). Turn off the gas and replace the tube. Make a drawing of the vertical section of the burner through the feed pipe [458]. d. Hold a dead match across the luminous flame close to the bottom, and examine the wood (?). Inference (?). Repeat with the non-luminous flame (?). Why is the interior of the flame cold? e. Is any gas entering or escaping from the holes at the base? To answer this, light a splint, blow the flame out, and hold the smoking end close to the holes (?). Hold the burner up and blow a sudden puff of air towards one of the holes (?). What is the effect of increasing the supply of air? 1 EXERCISE 2 Substances and Properties Object: To observe and record the properties of wool and of cotton. Apparatus: Graduated cylinder. Test-tubes, Rack. Evaporating dish. Wire gauze. Materials: 2 pieces each of white cotton cloth, white mixed goods, and woolen yarn. Sodium hydroxide (solution, 2%). Eosin or Acid Green (solu- tion, 0.5%). Sulphuric acid (cone, see Appendix V). H3'drochloric acid (cone). Ammonium hydroxide. a. Preparing the Cotton. In case the sizing [464, 580] has not been removed from the cotton cloth or the mixed goods, boil a piece of each material in 50 c.c. of water containing 2 c.c. of con- centrated hydrochloric acid. Rinse the goods in water, dip in 50 c.c. of cold water containing 0.5 c.c. of ammonium hydroxide, and rinse again. b. Place 60 c.c. of sodium hydroxide solution in the graduated cylinder. Divide the liquid equally between three test-tubes, immerse the pieces of cotton, wool, and mixed goods, one in each tube, and set the tubes in the rack. Attach the Bunsen burner by means of rubber tubing to a gas connection, and regulate the air suppl}^ so as to get a noiseless, non-luminous flame. Heat the contents of the tubes one after another to the boiling point, holding each by means of a test- tube holder or a piece of paper folded so as to Fig. 1. give four thicknessQS (Fig. 1). Then keep one above the flame, at the boiling point, but not bumping, for two minutes, then the second, then the third, then the first again and so forth. When the material in one of them has all dissolved, examine all three. Record the results as follows: Dissolved If Changed, Appearance of OR NOT HOW Liquid Cotton : Wool: Mixed goods: SUBSTANCES AND PROPERTIES c. Place the wire gauze on a ring on the ring stand (Fio-. 2). Fill the evaporating dish three-fourths full of water, add two drops of concentrated sulphuric acid, place it on the gauze and heat to boiling. Add 10 c.c. of the solution of the dye provided. Immerse one sample each of the cotton, wool, and mixed goods, so that they are completely covered. Stir with the glass rod, and heat for two or three minutes. Pour the liquid into the sink and wash the materials thoroughly in clean water. Note the effect on each (?). d. If a microscope is available, place shreds of each sample, after drying, on a strip of glass and describe the appearance of the fibers as to struc- ture (?) and color (?). e. Record the specific properties of wool and of cotton, both those observed in these experiments and those already known to you: natural color (?), natural structure (?), solubiUty in water (?), solubility in sodium hydroxide solution (?), effect of dyes (?). 3) Fig. 2. EXERCISE 3 Glass-working. Simple Bends Object: To learn how to bend glass and to make simple apparatus. Apparatus: Triangular file. Rack. Wing-top. Test-tube (hard glass) and stopper (1-hole). Materials : Glass rod. Glass tubing. a. Glass Rod. Make a transverse notch about 15 cm. (6 inches) from the end of a glass rod. To do this, hold the rod on the table and draw the edge of the triangle file once firmly and smoothly across it. Now, break the rod at this point by holding it so that the points of the thumbs are together on the side oppo- site to the notch, and pressing forward with the thumbs so as to bend the rod away from the mark. Cut two other pieces of the same length. To remove the sharp, often jagged edges, hold the ends of the rods in the Bunsen flame, turning them slowly until the edges are rounded (fire-polished). Observe the color of the flame (?). To what is this color due [526, 553]? Do not lay the hot rods on the table, but balance them across the test-tube rack or on an iron ring until cold. Why does heating the rods remove the sharp edges? b. Glass Tubing, Drawing Out. Cut, exactly as in a, from a piece of glass tubing a portion 15 em. long. Hold the center of this piece of tubing in the Bunsen i . — __iiq flame, turning it slowly, until it be- 1 ■-- ^-.. I comes soft (Fig. 3). Hold and turn it, as a whole, carefully, so as not to ■ ■ ] bend or twist it. When it is quite Fig. 3. soft, remove it from the flame, and draw the two ends slowly apart. If the result is satisfactory, reserve to make nozzle as directed in Exercise 4 b. 4 GLASS-WORKING. SIMPLE BENDS Right Wrong Fig. 4. c. Glass Tubing, Bending. To bend glass tubing, never use the ordinary Bunsen flame (why?). Place the wing-top on the burner, and use the resulting flat luminous flame of fish- (? ^;:^ tail form. Hold a piece of tubing 15 cm. long in the flame so that as long a por- tion as possible is heated, and rotate it steadily so as to heat all sides alike. Do not allow the tube to bend or twist. When the glass is quite soft, withdraw the tube and bend it to form a right angle, giving an L-tube (Fig. 4). The bend must be gradual and smooth, not sharp or crumpled. Bend another similar piece to form an obtuse angle. Fire-polish the edges (for this, use the non-luminous flame), but do not heat too long, otherwise the bore will be diminished. d. Fit a stopper into the hard glass test-tube. Remove the stopper, and push the shorter end of the obtuse-angled tube through the hole (Fig. 5). In inserting tubes in stoppers, always grasp the tube near the end to be inserted, for if force is applied at the far end of a long tube, the tube is apt to snap. Do not use much force — moisten the tube and the hole and rotate the tube while pushing it gently through (don't hurry). Allow the tube to project not over 1 mm. on the inside. Replace the stopper in the test-tube and test for air-tightness. To do this, place the end of the tube in the mouth, suck out some of the air, and note whether the tip of the tongue seems to adhere to the tube. Remove the test-tube, and repeat (?). What caused the tongue to adhere in the first instance? Fig. 5. EXERCISE 4 Construction of a Wash-Bottle Object : To construct a wash-bottle for use in later experiments. Apparatus: Bunsen burner. Glass and rubber tubing. Flask and cork to fit. Cork-borer. File. a. Select a good cork which will fit the mouth of the largest flask and soften it in a cork-softener or b}^ rolling it under the foot upon the floor while pressure is cautiously applied. Bore two parallel holes with the cork-borer, and smooth them by means of a rat-tail file. The cork borer is usually made of brass, and the edge is easily turned. Do not hold the cork against the table while boring, as the edge of the tool may be ruined. Hold the cork in the hand (or better, against a block of soft wood) and bore from the narrow end, with care, exactly parallel to the axis. If the cork and borer are rotated round their axes and the edge is fresh, very little force will be re- quired. Clear the core of cork out of the cork-borer, after use, by means of the iron rod. The borer is purposely chosen so as to be smaller than the tubing. Its use thus permits the enlarging and smoothing of the hole made in the cork "with the rat-tail file until a perfectly fitting bore has been made. b. Bend two pieces of glass tub- ing as indicated in Fig. 6, fire- polish their edges and insert them in the openings in the cork. Make the nozzle by softening a piece of glass tubing in the Bunsen flame, drawing the two ends apart after removal from the flame (Fig. 3), cutting in the center with the file, and fire-poUshing the 6 Fig. 6. CONSTRUCTION OF A WASH-BOTTLE 7 rough ends. Connect the nozzle by means of a short piece of rubber tubing. Test the apparatus to see that it is air-tight, as below. c. Place in the flask enough water to cover the lower end of the longer tube and transfer the rubber connection to the shorter glass tube and close it with a clamp. Now, blow through the longer tube so that a few bubbles of air pass into the flask. If the apparatus is air-tight the water will rise in this tube when the mouth is withdrawn and will remain in an elevated position (?). If the water gradually sinks to its former level, the apparatus is not air-tight. Examination of the holes in the cork may show defects, which can be remedied only by boring a fresh cork more carefully. A two-hole rubber stopper may be substituted for the cork, if desired. Try to make a good job of this exercise, so that 3011 won't have to be ashamed of yourself every time your assistant looks at your handiwork. A great many beginners are always optimistic enough to believe that they can bend glass tubing properly in a non-luminous Bunsen flame or without a wing-top, although they are definitely cautioned to the contrary in Exercise 3 c. Others can never see the necessity of rounding off the end of a glass tube before trying to insert it through a cork, until they have cut their fingers a few times. Time will teach both classes of offenders their error, and the laboratory assistant may also act as a catalyst. EXERCISE 5 Capacities of Vessels. Weighing and Density Object: To learn the capacities 0/ several vessels. To learn how to weigh and how to measure densities of liquids and solids. Apparatus: Burette. Beaker. Graduated cylinder. Test-tube. Flask. Balance (one to every 10 pupils). Thermometer (one for class). Materials : Distilled water. Roll sulphur. a. Fit a burette (Fig. 7) with a short piece of rubber tubing and glass nozzle (see Exercise 4 b). The withdrawal of liquid from the burette is regulated by a pinch clamp upon this rubber connection. b. Support the burette upon a ring- stand by means of a clamp. Now fill the burette with water, drawing off a portion to insure the complete removal of air from the rubber tubing and nozzle. The last bubble of air may be removed by turning the nozzle upward while the water is allowed to flow. Read the height of water by observing the lower side of the meniscus, or curved cx> 0= Vu: surface of the liquid (Fig. 8) . Keep the eye as near- ly as possible at the level of this surface while taking the reading (?), and esti- mate to tenths of a di- FiG. 8. vision. c. Clean and dry a small beaker carefully, weigh it on the balance to the nearest decigram (0.1 g.) and record the weight. In doing this, follow faithfully all the directions as to the proper WEIGHING AND DENSITY 9 use of a balance given you by your instructor, and write down these directions in detail in your book for future reference. Allow 10-20 c.c. of the distilled water to run from the burette into the beaker, read the new level of the water, and ascertain the volume taken by subtracting the readings. Weigh the beaker again and ascertain the weight of the water by subtraction. Take the temperature of the water by means of the thermometer. Cal- culate from your figures the weight of 1 c.c. of the water. The re- sult is the density of water at the recorded temperature. d. Weigh an evaporating dish (dry) on the balance to the nearest decigram (0.1 g.) and record the weight. Place in the dish about 10 g. of pieces of roll sulphur (no par- ticles or dust of sulphur), and weigh once more. Record the weight. The difference (?) is the exact weight of the sulphur actually taken. Place in the graduated cylinder exactly 20 c.c. of water. In- cline the cylinder and allow the sulphur gently to slide into the water in the cylinder. Read and record the total volume. The increase (?) is the volume of the sulphur. Calculate from your data the weight of 1 c.c. of sulphur (?). This is the density of the sulphur. e. Record the specific properties of sulphur which you have observed, namely: color (?), crystalline or not (?), brittle or malleable (?), density (?), soluble in water or not (?). Is measuring volume by burette or by cylinder more accurate and why? f. Measure by means of the cylinder, roughly, the volumes of water your flasks and beakers hold, and record the figures. Fill the vessels to a convenient height for use, and not to the brim. EXERCISE 6 Density Determinations and Experimental Errors Object: To determine more accurately the densities of a typical liquid and of a typical solid. To learn how to classify and evaluate experimental errors. Apparatus: Pycnometers. Bath regulated to 25" (one for class). Balance (one to every 10 students). Materials: Distilled water. Benzene. Powdered chalk. a. In Exercise 5 c you have determined the density of water by means of your burette. Is your result an exact value, or is it only a rough approximation? Refer to the temperature of the water recorded in your notes, and now compare your experimental result with that indicated by the curve* in Fig. 9. Suppose that your error in each reading of the meniscus in the burette might amount to 0.03 c.c, could that account for the whole difference between your value and the accepted one? What other errors might occur in the course of the experiment, and what are their respective magnitudes? Are you sure that your burette is cor- rectly graduated? It is no use doing a quantitative experiment unless you know to what extent you can trust your results. Errors may be divided into three classes: (a) errors of apparatus (such as an incorrect burette or a faulty balance), (b) errors of manipulation (such as reading the meniscus wrong through looking at an angle), and (c) errors of method (such as the impossibility of reading a burette more accurately than 0.01 c.c). The first class of errors you can diminish by standardizing or refining your apparatus, the second by working carefully and gaining the necessary technique, the third by modifj-ing the method. b. Suppose you wanted to obtain a really accurate value for the density of benzene at 25°. It would be futile to use the burette method. You employ instead a pycnometer, of the form illustrated in Fig. 10. After cleaning, drying and weighing the * Note carefully that in this curve the volume occupied by 1 gram of water is plotted against temperature. How can you transform these specific volume values to densities? 10 DENSITY DETERMINATIONS AND EXPERIMENTAL ERRORS 11 pycnometer, you fill it with distilled water, suspend it in a bath regulated to constant temperature at 25° and then by means of a piece of filter-paper at A draw the meniscus down on the other rVVTV c M?ose j f % 8 /-002a 8 y ^ /-0024 / y 1 1 ^ /-00/e / / / / h: /-00/2 / i Y ^ hoooe / / / h0004 J / y y V y HfOOO^ ^ r* L V* n k-^ n ',' 2 0"" d r z t Temperature - C Fig. 9. — Change of Volume of Water with Temperature. side exactly to the mark B. Removing the pycnometer from the bath, you carefully dry its outside surface, and reweigh it. After that you repeat the determination, using benzene instead of water. Subtracting the weight of the empty pycnometer from the two subsequent weights gives you the weights of water and of benzene respectively required to fill the instnmient to the mark 12 DENSITY DETERMINATIONS AND EXPERIMENTAL ERRORS B at 25°. The ratio of these weights, wt. of benzene/ wt. of water, is the specific gravity of benzene referred to water at 25°. To get the absolute density (grams in 1 c.c.) of benzene at 25°, you have n "^ ^ Fig. 10. Fig. 11, to multiply the specific gravity, as obtained above, by the den- sity of water at that temperature (0.9971, see Fig. 9). c. If the substance you have to investigate is a solid insoluble in water, such as chalk (calcium carbonate [560], not blackboard crayon, which is mainly calcium sulphate [564]), you use a pycnometer of a different type, shown in Fig. 11. As before, you find the weight of this (a) when empty, and (6) when filled with water to the mark C. You^next powder up some of your solid very finely in a mortar, introduce a few c.c. of the powder into the empty and dry pycnometer, and weigh again, (c). Fi- nally, you add water to this, agitate to remove all air-bubbles, adjust to the mark at constant temperature, and reweigh, {d). Suppose your results were as follows: (a) Wt. of pycnometer empty = 10.03-^ g. (6) " " " + water = 30.100 g. (c) " " " + chalk = 25.210 g. (d) " " '■ -h chalk + wat«r = 39.t)80 g. DENSITY DETERMINATIONS AND EXPERIMENTAL ERRORS 13 How can you derive the density of chalk from the above data? Well, subtracting (a) from (6) tells you that the pycnometer holds 20.065 g. of water. Subtracting (a) from (c) tells you that 15.175 g. of chalk were used in the determination. Sub- tracting (c) from (d) shows that the pycnometer will hold only 14.470 g. of water when this amount of chalk is present. 15.175 g. of chalk, therefore, displace or occupy the same space as 20.065 — 14.470 = 5.595 g. of water. The specific gravity of chalk is consequently 15.175/5.595, or 2.712. If all the fillings were done at 25°, the density of chalk would be 2.712 X 0.9971, or 2.704. The final result, you will notice, stops at the third place of decimals, al- though by actual multiplication of the two previous values we could obtain a much more formidable answer. One of the most important things for you to know in all quantitative work and in all numerical problems is when to stop ■figuring. Many students never try to get this straight, but fill page after page of their notes with calculations carried out to ridiculous lengths. If you insist upon doing this in your quizzes, do not be astonished if 90 per cent of your answers turn out wrong. Never take any calculation beyond your probable limits of error. How can you tell when to stop? To simplify matters, let us assume that you do not want to ascertain more than the order of magnitude of your inaccuracy. Suppose we return to the experiment on chalk described above. You were obviously weighing to the nearest 0.005 of a gram. Your probable error in the difference between any two weighings therefore approximates this weight as a limit. To get the sp. gr. of the chalk, you found the quotient of two such differences, 15.175 and 5.595 g. The percentage error will be greater in the smaller of these values, namely about one-tenth of one per cent. Unless any other error involved in your work is proportionately greater,* this is the limit to which you are entitled to take your final answer. You do not, therefore, wTite down the sp. gr. as 2.7122, since this would infer that your value was accurate to less than 1 part in 20,000! Neither do you stop at 2.71, since that would not be giving yourself a square deal for the trouble you have taken in the experimental work. One place beyond the last figure of which you are absolutely certain is always ample. When you multiply or divide two values, the lower limit of accuracy prevails. Go back now to your calculations in Exercises 5 c and 5 d and strike off the superfluous figures in your final density values. Note what a lot of extra work you made for yourself, and try to avoid similar mistakes in future experiments. * For very accurate work, correction must be made for the weight of air displaced in each observation, and the degree of accuracy to which the meniscus can be adjusted in the pycnometer must also be established. EXERCISE 7 Changes in Metals Heated in Air Object : To observe changes in properties when a new substance is formed by the action of oxygen from the air. Apparatus: Balance. Porcelain crucible. Pipe-stem triangle. Meter stick (one for class). Piece of iron wire (No. 26). Materials: Copper wire (No. 30). Tin foil. a. Take about 5 meters of copper wire (No. 30), wind it into a coil around a pencil, and place the coil in the porcelain crucible, which has previously been weighed (uncovered). Weigh the whole on the balance, recording the weights as in 5 c. Place the crucible (uncovered) in the pipe-stem triangle (Fig. 12) and heat, at first gently and then with the full Bunsen flame, for fifteen minutes. Now lower the flame to permit the crucible to cool gradually, and finally remove it. Weigh the cruci- ble when cold (?). To what is the dif- ference in weight due? ^ \ Examine the coil (?), and bend the / —A remains of the wire (?). Name the ^ ...^ product, and make a condensed state- ment [24] vof the change. Record the specific properties of the copper and of the product, namely: color (?), appearance (lustrous or otherwise?), pliability or brittleness (?) of each. Why is the result of this experiment not reliable quantitatively? Devise improvements in the method of carrying out the experiment which would enable you to obtain a quantitative result [40]. What happens when copper is heated in the absence of air or oxygen? Devise a means of proving that the presence of air or oxygen is necessary for any chemical change to occur. U CHANGES IN METALS HEATED IN AIR 15 b. Fold up about 10 cm. square of tin foil and place it in the porcelain crucible. Weigh the whole on the balance and proceed as in a, par. 1. Stir the tin occasionally with a short piece of iron wire, but be careful to keep all the material in the crucible. Describe what you observe (?). Name the product (?) and make a condensed statement [24] of the change. Record the specific properties of the tin and of the product, namely, color (?), appearance (?), pliability (?) of each, and melting point of tin [539] (?). Is the result of this experiment quantitatively rehable? If not, why not? Suggest methods of improvement. c. Slow Oxidation of Metals. Devise a way of showing that air loses a part of its substance (not, e.g., that the iron gets heavier, but that the air diminishes in amount) when moist iron powder rusts, and try it. Submit your arrangement to the instructor for criticism before using it. EXERCISE 8 Mixtures and Compounds Object: To learn how, hy observing properties, to distinguish between mixtures and compounds. i^pparatus: Magnet. Test-tubes. Funnel. Watch-glass. Mortar. Trip scales. Bunsen. Materials: Iron powder. Carbon disulphide. [Caution: Extinguish Bunsen flame while using this.] Filter-paper. Hydrochloric acid (dil., see Appendix V). Sulphur. a. The Properties of Iron. Place about 0.5 c.c. of iron powder on a piece of paper. Examine it (?), Draw one pole of a magnet across the lower surface of the paper^ noting the behavior of the iron (?). Transfer half the iron to a dry test-tube, add 2 c.c. of carbon disulphide [CARE! Inflammable! Do not handle near a flame], and shake. Fold a filter-paper once, and then again at right angles to the straight edge. Open the paper as a cone, with a triple layer of paper on one side and a ^\~/ \ / single layer on the other, and ^ V place it in a glass funnel (Fig. 13). Place the funnel in one p -o ring of the iron stand, place the watch-glass below the end of the stem, and pour the contrnts of the tost-tube on to the paper. When the liquid has run through, open up the paper, so that the remaining liquid may evaporate. Place the watch-glass in a draft, away from all flames, where its contents may evaporate also. While evaporation is going on, proceed with the operations I described in the following paragraphs. When the paper and watch-glass are dry, examine the residue on the paper (?) and draw the pole of the magnet across the lower surface of the paper (?). Examine the watch-glass (?). Is iron soluble in carbon disulphide (?). 16 MIXTURES AND COMPOUNDS 17 Place the other haK of the iron in a test-tube, add a few drops of hydrochloric acid (?) and note the odor [609] or absence of odor. Record the properties of iron, namely: color (?), effect of magnet (?), solubility in carbon disulphide (?), effect of hydro- chloric acid (?) and odor of the evolved gas (?). b. The Properties of Sulphur. Pulverize some sulphur in the mortar, and repeat a, using about 1 c.c. of sulphur instead of the iron. Record the properties of sulphur, additional to those already recorded in Exercise 5 e, namely: effect of magnet (?), soluble in carbon disulphide or not (?), shape of crystals (sketch ?), effect of hydrochloric acid (?) and odor or not (?). c. On a piece of paper weigh out 3 g. of pulverized sulphur and 5.0 g. of iron powder. Mix the powders as well as possible. Can the particles of each substance still be recognized or not? Pass the magnet underneath the paper (?). Place half the mix- ture in a test-tube, add 3^ c.c. of carbon disulphide, shake, and filter into the watch-glass. When the liquid has evaporated, examine the residues on the paper and in the watch-glass (?). Why does the result show that the material was a mixture and not a chemical compound? d. Place the remainder of the mixture from c in a dry test- tube, hold the test-tube by means of a test-tube holder or a piece of folded paper (Fig. 1, Exercise 2), and heat it gently in the Bunsen flame until all action has ceased (?). When the test-tube is cold, place the lower end in the mortar, cover with a towel, and use the pestle to strike through the towel so as to break the test-tube (?). Continue in this way until the material which was in the tube, separated as far as possible from attached fragments of glass, can be placed in another test-tube. Add 2 c.c. of carbon disulphide, filter, and allow the filtrate to evaporate as before. Examine the material on the filter to ascertain whether it is iron (?), If it is in the least affected by the magnet, too Uttle sulphur was used. Does the filtrate >deld all the sulphur used (?), or any sulphur? Place the material on the filter in a test-tube, add a few drops of hydro- chloric acid (odor? [326]). Did either iron or sulphur give this odor? Record the properties of the new substance, ferrous sulphide, 18 MIXTURES AND COMPOUNDS namely: color (?), effect of magnet (?), solubility in carbon disul- phide (?), effect of hydrochloric acid (?) and odor of the evolved gas (?). What was the effect of heating the mixture? Is the product an element or a compound, or a mixture? Write a con- densed statement [31] for the reaction. What variety of chemical change is illustrated in this experi- ment? What evidence of a chemical change is afforded beside the formation of a new substance? e. (Optional.) Gunpowder is made from saltpeter (potassium nitrate), roll sulphur, and charcoal. Take specimens of these three substances, and examine them with respect to properties which can be used for recognition and separation, such as appearance and solubilit}^ in various solvents. Try the solubility of each in distilled water and in carbon disulphide, using in the latter case thoroughly dried (why?) test-tubes. Do not judge of solubility by the eye, but filter the mixture, catch a few drops of the hquid on a watch-glass, evaporate, and see whether there is any greater stain on the glass than the pure solvent would itseff have left. The taste (?) of the saltpeter is a characteristic property. Now place about 1 g. of gunpowder in a large test-tube and add 5-10 c.c. of water. Shake well (after closing the test-tube with the thumb), warm gently, and filter. Evaporate the filtrate upon a water bath or over a beaker of boiling water (Fig. 15, p. 31). Describe and name the residue (?). Dry (why?) the filter paper and its black contents over a radiator or in a drying oven. Shake the dried product with cold carbon disulphide in a dry test-tube, filter, and allow the filtrate to evaporate [HOOD] spontaneously (?). What remains upon the paj^er? Did any chemical change occur during the manufacture of gunpowder? Are the three substances components or constituents of gunpowder? Is the latter a mixture or a compound? Why are the ingredients of gunpowder pulverized so finely and mixed so intimately? 1^ EXERCISE 9 Composition and Formula of Nickel Sulphide Object: To find the composition and formula of nickel sulphide {quantitative). Apparatus: Porcelain crucible and cover. Balance. Pipe-stem triangle. Materials: Nickel, powdered {" reduced "). Flowers of sulphur. a. Weigh the crucible (without cover) to the nearest centi- gram. Place about 2 g. of reduced nickel (do not attempt to take this amount exactly) in the crucible and weigh again. Put about 2 g. of sulphur in the crucible, stir the contents, and place the crucible on the pipe-stem triangle. Set the cover on the crucible, and heat gently so long as sulphur vapor burns [HOOD] at the chink between the crucible and cover. Heat strongly for 1-2 minutes. Then hold the flame against the upper portion of the crucible, so that every part receives a thorough heating. Allow the crucible to cool. When it is cold (not before) remove the cover and weigh. Tabulate the results as follows: Wt. of crucible + nickel g Wt. of crucible empty g Wt. of nickel taken g Wt. of crucible + nickel sulphide g Wt. of crucible + nickel g Wt. of sulphixr combined g Wt. of crucible + nickel sulphide g Wt. of crucible empty g Wt. of nickel sulphide g b. Calculate the percentage composition: wt. of sulphur X 100 „ Per cent sulphur = wt. of nickel sulphide T, ^-11 wt. of nickel X 100 „ Per cent nickel = -- — ^ — —. — -, — , , . . = ? wt. of nickel sulphide 19 20 CX^MPOSITIOX AND FORMULA OF NICKEL SULPfflDE c. Find the empirical formula of nickel sulphide. To do this, first obtain the atomic weights of nickel and sulphur from the table (Appendix II). Wt. of sulphur -7- at. wt. of sulphur = ? (factor 1) Wt. of nickel -i- at. wt. of nickel = ? (factor 2) The combining proportion of sulphur to nickel found in the ex- periment is therefore: At. wt. sulphur X factor 1 _ S X factor 1 At. wt. nickel X factor 2 ~ Ni X factor 2 Divide above and VxjIow by the smaller of the two factors (?). What is the formula? d. Make the equation for the union of sulphur and nickel to form nickel sulphide. Exerciftes 9 and 10 are Vx>th quantitative. P^ememh>er that if you get an abwjiutely irrifxjssible result you will probably \)e asked to repeat your work. Take every precaution note^l in the Oudirt/:, therefore, to decrea«fj the risk of error. If you lose any apprec:iable amount of material by spattering in 10, it will pay you to start all over again rather than to hand in a result which is sure to \)e wrong. It is not likely that what follows will affect you personally, but you had Ijctter read it anywaj-. However discouraging it may \je to know in advance that your answer is going to \)e unacceptable, on no account yield to the temp- tation to " manipulate " it. You may think that you know what the result ought to h>e by working backwards from the formula, and it seems so much easier t^j hand in a correct " calculated " value than to go right through the mef:hanical details of the experiment again. \'ou might fxjssibly get by once or twice with a c^xjked result, but it is not worth the risk, "i'ou never know when your instructor may slip Htmiftt^'mg over on you by suhMituting a different sul^stance from that mentioned in the text. It nec^ls a lot of exjjeri- ence, furthermore, to fake an experiment successfully. P'requently, your laboratfjry notes will make it quite evident that you could not possibly have got the result that you claim, and then woe Ixitide you. KememF>er Dr. Cook of North Pole fame. II©' was an expert faker, but his own tkAoh gave him away in the end. Enough said upon an unpleasant subject. ► EXERCISE 10 Composition and Formula of an Oxide of a Metal Object : To find the proportions of tin and oxygen in oxide of tin, or of iron and oxygen in an oxide of iron, and the formula of each compound (quuntitative) . Apparatus : Porcelain crucible. Balance. Pipe-stem triangle. Evaporating dish. Beaker. Materials: Tin foil (free from lead). Pure iron (piano-) wire. Nitric acid (cone, and dil.). a. Weigh the crucible (without cover) (?). Place in it about 1 g. of tin foil (do not try to take exactly 1 g.) and weigh again (?). Record the weights in tabular form (see below) . Place the crucible on the pipe-stem triangle and add 5 c.c. of concentrated nitric acid. In doing this, pour the acid over every part of the metal. Hold the burner in the hand and warm the crucible with a very small flame, stopping for a moment if there is a tendency for any particles to be spattered out of the vessel. When the contents are dry, use a larger flame and heat for ten minutes. Weigh when cold (?). The nitric acid oxidizes the tin. A brown gas (nitrogen tet- roxide [413]) and water are given off during the process. Be careful not to get any of the issuing gases into the lungs (?). Wt. of crucible + tin Wt. of crucible, empty Wt. of tin taken g, Wt. of crucible + oxide of tin g Wt. of crucible + tin g Wt. of oxygen g, Wt. of crucable + oxide of tin g Wt. of crucible, empty g, Wt. of oxide of tin g. Calculate from your results the percentage composition of the oxide of tin. 21 22 COMPOSITION AND FORMULA OF AN OXIDE OF A METAL Find the atomic weight of tin in the table (Appendix II) and calculate the formula of the oxide. b. Composition of an Oxide of Iron. Weigh an evaporating dish of medium size, place in it about 1 g. (12 inches) of pure iron wire, and weigh again. Cover the dish with a watch-glass, convex side downward, and add 10 c.c. of pure dilute nitric acid. Set the dish, covered, on a water bath (see Fig. 15, Exercise 14) until the iron has dissolved, adding a few drops of concentrated nitric acid if any of the wire remains unattacked (Instructions). Then rinse any material on the cover-glass carefully into the dish with the help of your wash-bottle and evaporate the solution to dry- ness. When the residue is dry, place the dish on a clay triangle supported on the ring-stand and heat carefully with a burner held in the hand as long as any red fumes are given off. During this process, and especially at first, great care and patience must be exercised, as too rapid heating may cause sohd particles of the product to be thrown from the vessel. If any crackling noise is observed, remove the burner at once. When, after final strong heating of every part of the material, red fumes or other evidence of continued change can no longer be perceived, allow the dish and contents (?) to cool, and then weigh. To make sure that the decomposition was complete, heat once more, cool, and weigh again. This precaution is always necessary in experiments of this nature. The difference of the weights of the metal and of the oxide gives the weight of oxygen combined with the known weight of iron. Assuming the atomic weights of iron and of oxygen to be 55.9 and 16, respectively, calculate fron\^your data the fornmla of the oxide of iron. What is the name of this oxide? What other oxides of iron are known? Calculate the percentage composition of the oxide of iron repre- sented by your formula and compare this percentage with the actual composition you obtain from your work. EXERCISE 11 Oxygen — Preliminary Object : To learn which substances yield oxygen, and how to recognize it. Apparatus: Test-tube (hard glass). Clamp. Porcelain crucible. Materials: Mercuric oxide. Wooden splints. Sand. Potassium chlorate. Manganese dioxide (powdered). Sodium peroxide. Litmus papers. a. Place about 1 c.c. of mercuric oxide (properties ?) in a' dry hard glass test-tube, and fasten the tube in an inclined position in the clamp on the iron stand. Heat at first gently and then strongly with the Bunsen flame. Introduce a wooden splint, glowing at one end, into the tube until the spark almost reaches the oxide (?). What gas is liberated? What physical and chemi- cal properties do you observe the gas to have? After removing from the flame, examine the residue on the side of the tube (?). How did it get there? Name the variety of chemical change illustrated [32]. b. Repeat a, using 1 c.c. of silicon dioxide (sand), and answer the same questions. c. Repeat a, using 1 c.c. of potassium chlorate (properties ?), and answer the same questions. d. Repeat a, using 1 c.c. of manganese dioxide (properties ?), having previously dried this by warming it in the porcelain cru- cible.* Answer the same questions. e. Place in a dry test-tube about 0.5 c.c. of sodium peroxide. Detach the nozzle from your wash-bottle (Exercise 4 b), fill it with water, hold your finger over the open end, and release for a moment, to add one or two drops of water to the peroxide (?). Test this gas with a glowing splinter of wood (?). Afterwards, dip a piece of red litmus paper in the residual liquid (?). A blue color indicates the presence of an alkali [206] (sodium hydroxide). * Be sure to dry your sample of manganese dioxide before heating it strongly, since most commercial samples contain an appreciable quantity of water, and the condensation of drops on the side is liable to crack the tube. Unless you have a very good blast-lamp, you will probably be unable to note any evolu- tion of oxygen from this substance [79]. 23 EXERCISE 12 Oxygen — Preparation and Properties Object : To make a rpjantity cf oxygen and to aacertain Us jthy triad and chemical iiTf/ffffriiesi. Apparatus: Mortar. Trip sicales. Test-tube. Te«t-tube /'hard glaae) with stopper and \yent tube ''Exercise 3 d). Narrow rubf^er tube 12 in. long. Clamp. Pneumatic trough. 3 wide-mouth bottles, 'i glass plates. De- flagrating ifjfOfm. Materials: Potassiimi chlorate. Manganese dioxide ^powdered*.* Splints. Sulphjir. lie^l phr>«phorus. Charcoal ^.^plintersj. a. Take 4 g. of finely-powdered potassium chlorate. Mix it thoroughly on paper with 2 g. of manganese dioxide. (To avoid accidents, the latter should \)e carefully heated in an open dish, with stirring, to free it from car^xjnaceous matter hjefore use.) Place about one-tenth of the mixture in a dry test-tube, heat it, and test the gas with a glowing splinter of wood (?). How does the temperature at which this mixture gives off oxygen compare with the temperature at which each substance would j-ield oxygen if heated alone (Exerci.se llj? Why is the manganese dioxide used? What is a substance which behaves in this way called? De\n.s^ a way of showing that the manganese dioxide, used as in a, remaias unchanged after the action, and that it is the potas- sium chlorate that losf^ its oxygen, and try it (?). Con.sult the instructor in regard to the details oLyour plan before e.xecuting it. b. Place the remainder of the mixture made up for a in the hard glass test-tube provided with a stopper and glass tube (Ex- ercise; 3 d;, and test for air-tightness. Moi.sten the end of a piece of narrow nibhjer tubing (^2 in. long; and slip it over the end of the * Ferric oxide may be conveniently substituted for manganese diojcide as a catalyst in KxcTrifft 12 sl It la morfi efficient, it does not neerl to be dried in advance, and it«j di.stinctive color is a safe-guard against accidents. A carelem student might easily lise powdererl charcoal in.«rtead of manganese dioxide in this exyjeriment and the results would be very distressing. 24 I OXYGEN — PREPARATION AND PROPERTIES 25 tube. Clamp the tube in a horizontal position (Fig. 14). Fill the pneumatic trough with water so as to cover the sheK or other support. Fill 3 wide-mouth bottles with water, cover them with glass plates, and invert them, one on the shelf, and the other two in the trough. Use a small Bunsen flame to heat the tube and collect the first bubbles of gas in a test-tube filled with water and inverted over the exit of the rubber tube. Test this gas A^ith a Fig. 14. glowing splinter (?). What is this gas, and where did it come from? Now fill the bottles one by one, covering each when full with a glass plate, and setting it mouth upwards on the table. During the operation, regulate the flame with great care so that the gas comes off in a steady, but not too rapid stream of bubbles. If the gas begins to come too fast, move the flame promptly to another part of the material and lower it slightly. The glass must not become hot enough to tinge the Bunsen flame yellow. Do not remove the flame, however, at any time, without first taking the rubber tube out of the water (Why?). After the third bottle is filled, remove the rubber tube from the water, let the test-tube cool and then fill it with water and set it aside. 26 OXYGEN — PREPARATION AND PROPERTIES c Place in the deflagrating spoon a little sulphur. Heat the sulphur until it catches fire. Observe the flame for a moment (?). Then lower the spoon into one bottle of oxygen (?), keeping the bottle as far as possible covered with the glass plate. How does the flame differ from that in air, and why? Is it finally extin- guished? If so, why? Cautiously note the odor (?). Name the product (?) and state its physical properties (?). d. Empty the spoon (burning off any sulphur left upon it), let it cool, and place on it a little red phosphorus. Set fire to the latter, observe the flame (?) and lower the spoon into the second bottle as before (?). Name the product (?) and state its physical properties (?). Before using the spoon in e, heat it strongly in the Bunsen flame to burn up all the phosphorus. e. Lay a splinter of charcoal in the bowl of the deflagrating spoon, hold in the Bunsen flame until the charcoal begins to glow, and lower the spoon into the third bottle as before (?). How does the combustion of charcoal in oxj-gen compare with that in air? Name the product (?) and state its physical properties (?). f. Record the physical properties of oxygen: color (?), odor (?), solubility in water (?). Record the chemical properties: glowing spHnt (?), sulphur (?), phosphorus (?), charcoal (?). What is the difference between a chemical and a physical property? Write balanced equations for the reactions that occur in a, c, d, and e. g. (Optional.) Repeat a, substituting other oxides for man- ganese dioxide, in order to obtain an approximate indication as to the relative efficiency of each as ^ catalyst for the decomposition of potassium chlorate. Suggested oxides for this experiment are ferric oxide, chromic oxide, aluminium oxide, cupric oxide and siHcon dioxide. Is oxygen the only^gas evolved when potassium chlorate is heated in the presence of the above oxides, or can j^ou detect any other gaseous product? What properties of this second product enable you to distinguish it from oxygen (refer to Exercise 25)? EXERCISE 13 Weight of' a Liter of Oxygen* Object: To learn the weight of a measurable volume of oxygen. Also to make the necessary corrections and calculate the density of this gas under standard conditions (quantitative). Apparatus: Trip scales. Porcelain crucible. Iron wire. Hard glass test tube with 1-hole stopper, bent tube and narrow rubber tubing, ^-liter bottle. Trough. Thermometer (one for class). Barometer. Glas& plate or cork. Balance. 500 c.c. graduated cylinder (1 for 10 pupils). Materials: Manganese dioxide (powdered, dried). Potassium chlorate (chemically pure, powdered, dry). a. Place 6 g. of pulverized manganese dioxide (or ferric oxide, see footnote to preceding exercise) :n. the porcelain crucible (un- covered) and heat it with the full Bunsen flame for 5-6 minutes to drive off all moisture (see Exercise 11 d) . During this time, stir it occasionally with an iron wire. While this is going on, insert an obtuse -angled tube in a one- hole rubber stopper which fits the hard glass test-tube (as in Fig. 5, Exercise 3 d) . Fill a 2-liter bottle with water, invert it in the pneumatic trough, and arrange the apparatus as in Fig. 14, Exercise 12. Take 7 g. of dry, pulverized potassium chlorate and, when the manganese dioxide has cooled, mix the two substances thor- oughly on a sheet of paper. Place the mixture in the hard glass test-tube. Weigh on the balance the test-tube and contents to the nearest centigram and record the result according to the table on p. 28 (?). Replace the stopper in the test-tube, and test for air-tightness (see Exercise 3 d) . b. Heat the contents of the test-tube, beginning at the end next to the stopper (be careful not to burn the stopper (?)), and collect all the gas in the bottle. Regulate the heating so that * This experiment may be deferred, if desired, so as to form an immediate practical introduction to Exercise 20. 27 28. WEIGHT OF A LITER OF OXYGEN you can at all times count the bubbles. Continue heatino^ until gas ceases to come off, and then rcMuove the rubber tube from the water and allow the test-tube to cool. Lower the bottle of gas in the trough until, when the eye is on a level with the water, the latter is seen to be at the same height inside and outside. To accomplish this and the next operation, it may be necessary to incline the bottle slightly, taking great care not to let any bubbles of gas escape. While the bottle is in this position, close it with a cork or glass plate and set it mouth upwards upon the table. Read and record the tem- perature of the water (?) and also the barometric pressure (?). If, at this point, there is not time to complete the experiment, the test-tube may be corked tightly and put away (upright) along with the 2-liter bottle and its contents. c. Weigh on the balance the test-tube and contents, and record the weight (?). To measure the volume of gas collected in the bottle, fill the 500 c.c. graduated cylinder to the top of the gradua- tion, note down the volume of water, and pour the latter into the bottle. Repeat until the bottle is filled level with the mouth, and record in the table the total volume of water used. Wt. of test-tube and contents before heating g. Wt. of test-tube and contents after heating g. • Wt. of Oxygen g. Volume of Oxygen c.c. Temperature C. Barometric Pressure mm. Tension of aqueous vapor [Appendix I] mm. Barometric pressure, correctea [99] mm. d. Reduce the observed volume of oxygen from the o})scrved Temperature and pressure to 0° and 760 mm. [95-9]. e. From this reduced volume, and the weight, calculate the weight of 1 c.c. (the density) of oxygen. Wt. of oxygen vol. at 0° and 7()0 nun. = X = wt. of 1 c.c. = densitv Exercise 13 is quantitative, and if you depart from the diroctions, you do so at vour own risk. There's a reason for every precaution > ou are told to take. WEIGHT OF A LITER OF OXYGEN 29 In this experiment, the following points are of particular importance, (a) Dry your manganese dioxide or ferric oxide carefully before you mix it with the potassium chlorate; otherwise when j^ou weigh the mixture you will weigh some water as well, and the loss of weight on heating will not be due entirely to evolution of oxygen. (6) Use a hard glass test-tube; one of soft glass will fuse and spoil the experiment, (c) Make absolutely sure the apparatus is air-tight, using the method recommended in the text. If there is a leak, it will probably be between the test-tube and its cork, since the weight of the rubber tube introduces a strain at this point. Try to arrange matters so that your cork, without being in any sense too small, fits well into the test-tube. If it will not do so, go up to the stock-room and ask for a test-tube stretcher. Then return to your desk and bore another cork, (d) Heat very cautiousl-y at first or the oxA'gen evolved will contain small particles (" smoke ") of potas- sium chlorate. Why will this spoil results? (e) Be careful not to have a suck- back of water from the trough into the test-tube at any stage of the experiment. How can you avoid this? (/) Do not lose any gas from the bottle in equaliz- ing ,the levels inside and outside. Why is this step necessary'? What errors can you locate in this experiment, as you have carried it out'/ Subdivide them into errors of apparatus, manipulation and method, as di- rected in Exercise 6 a, and estimate the approximate magnitude of each What is the probable error in your final result? How would you modify your experimental procedure so as to diminish this error? EXERCISE 14 Hydrogen — Preliminary Object: To learn various ways of obtaining hydrogen and to compare them. Apparatus: 12 test-tubes. Graduated cylinder. Evaporating dish. Watch- glass. Beaker. Ring stand. Wire gauze. Materials: Iron (nails). Zinc (gran.). Tin (gran.). Copper (shavings). Aluniinium (wire). Magnesium (ribbon). Hydrochloric acid (cone). Zinc (dust). Sulphuric acid (dil. and cone). Acetic acid (dil., see Ap)- pendix V). Calcium.* a. Place in separate test-tubes a few small pieces of each of the metals: iron (nails), zinfc (granulated), tin (granulated), copper (shavings), aluminium (wire), magnesium (ribbon). Pour from the graduated cylinder 20 c.c. of pure concentrated hydrochloric acid [115] into a small beaker, add an equal volume of water, and mix. Add 5 c.c. of this diluted acid to the contents of each tube. Observe each case critically, and tabulate the results. Is there bubbling? If not, then warm gently (?). If the eye detects the formation of a gas or vapor, smell the contents of the tube (?). For comparison, take 5 c.c. of the acid by itself in a test-tube, smell it (?), warm and smell again (?). If heating seems to pro- duce a gas, remember that it may bo the acid, or steam, and not hydrogen. The formation of hydrogen may be inferred from continued bubbling when heat is not being furnished, and may be proved by the slight explosion which follows when a light is brought to the mouth of the tube. If the gas is coming slowly, hinder its escape into the air by partially closing the mouth of the tube and let it accumulate before applying the light. Number the metals in your notes in the order of their apparent activity (most active = No. 1). Do the bubbles appear on the side of the glass tube or on the metal? Why do they appear on one and not on the other? Record the properties of hydrogen * Calcium (metal) is most easily broken into small pieces by fixing it in a vise and using a chisel and hammer. 30 .'>-V'^^ HYDROGEN — PRELIMINARY 31 you have observed: Gas, liquid or solid (?), soluble in water or not (?), colored (?), odor or nor (?), unites with oxygen from the air or not (?) and if so when cold or hot (?). b. After the action has ceased, filter any one of the solutions and evaporate 1 c.c. of it to dr>^ness as follows [HOOD] (?). Place the watch-glass on a beaker half filled with water, set the beaker on the wire gauze and boil the water (Fig. 15). If the water in the beaker runs too low, because of evaporation, the vessel may crack. Add more hot water, if necessary. What is the solid left on the watch-glass by evapora- tion? c. Add some zinc dust, made into a paste with water, to the remaining 5 c.c. of the acid (?). To what is the difference, if any, between the apparent activity of zinc dust and granulated zinc due? d. The same metals displace hydrogen from all acids. To illus- trate, place a few pieces of zinc (gran.) in each of two test-tubes and add to one 5 c.c. of dilute sul- phuric acid (?) and to the other 5 c.c. of acetic acid (?). e. Now compare (?) the behavior of concentrated sulphuric acid with that of the diluted acid used in d, by placing some zine (gran.) in a test-tube and addin^nough of the concentrated acid barely to cover the metal (?). After noticing the effect in the cold (?), apply heat (?). Odor (?). What products are formed [326, 344]? f. Fill a test-tube with distilled water, and invert it in a large beaker half filled with water. Place a small piece of calcium in the water and hold the test-tube over it (?). After the action has ceased, apply a light to the gas in the tube (?). Examine the water in the beaker (?) and test it with red litmus paper (?). Fig. 15 32 HYDROGEN — PRELIMINARY Write balanced equations for the reactions that occur in a, d; e and f. If Exercise 14 a could be carried out under standard conditions, you would obtain reactions varying in speed according to the position of the metal in the activity series [123]. But standard conditions are difficult to arrange, and 3'our results will be affected by such factors as (a) the rate at which the acid can remove surface oxides, (b) the state of division of the metal, and (c) the nature of the impurities in the metal. For a more detailed discussion of this last effect, see [225]. The hydrogen obtained from zinc and dilute sulphuric acid in 14 d may not 1^ odorless, owing to non-metallic impurities in the zinc (compare ExercLse 8 a). Do not allow this, however, to cause you to miss the different and very characteristic odor encountered in 14 e, where concentrated sulphuric acid is used. Evidently the nature and the concentration of the acid are just as imi)ortant in regulating the rate of hydrogen evolution as the nature of the metal, '^'ou will see exactly why this is so later [274, 344). Exercise the greatest care in all experiments involving hydrogen. Never, under any circum-stances, attempt to light a jet of the gas until you have made absolutely- sure that all air has been swept out of your apparatus. To be I)Ositive upon this point, you must have obtained a sample in a test-tulxj which bums quite quietly (Exercise 15). If you have any doubt at all, consult your laboratory assistant. An explosion during a hydrogen preparation is a sign of criminal carelessness, and you will get no sympathy however badly you may be hurt. Whether you are removed from the laboratory whole or in sections, you deserve to be removed permanently, as a menace to your innocent neighbors. u EXERCISE 15 Hydrogen — Preparation and Properties Object : To prepare a quantity of hydrogen and observe its physical and chemical properties. Apparatus: 90 c.c. gas-generating bottle with 2-hole stopper and thistle- tube. Glass tubing. 12-inch narrow rubber tube. Trough. Trip scales. Test-tubes. 2 wide-mouth bottles and 2 glass plates. Beaker. Taper. Materials: Zinc (gran.). Sulphuric acid (cone). a. Fit the 90 c.c. gas-generating bottle with a 2-hole stopper, a thistle-tube, and an L-tube (Fig. 16). Shp the narrow rubber tube over the end of the last. Place in the bottle about 20 g. of zinc (gran.). Test the apparatus to see whether it is air-tight. To do this, pour into the bottle through the thistle- tube enough water to cover the zinc. The lower end of the thistle-tube must also be under the water. Now blow through the rubber tube a little air, so as to force the water up the stem of the thistle-tube, and immediately compress the rubber tube with the thumb and forefinger. If the water does not re- main stationary, but gradually falls, there is a leak which must be remedied [Instructor]. Add concentrated sulphuric acid slowly through the thistle-tube until brisk bubbling sets in. Do not add more than one-fourth of the volume of the water already in the bottle. Place the end of the delivery tube in the trough. Collect a test-tube full of the gas. Close the tube with the thumb and carry it mouth downwards to a distant flame. (Under no circumstances bring a flame near the generator of the delivery tube!) Remove the thumb and, still holding the tube mouth downwards, set fire to the gas. Repeat this test until a sample is obtained which burns quietly. Why does it not do so at first? Do not at any time attempt to light the gas at the exit tube. 33 Fig. 16. 34 HYDROGEN — PREPAK\TION AND PROPERTIES b. Collect over water two bottles of the gas. Cover the first with a glass plate and set it mouth downwards on the table (?). Light a taper, raise this bottle (still mouth downwards), insert the burning taper (?) almost to the bottom of the bottle (?) and then withdraw it slowly (?). What happens to the gas? What happens to the taper on insertion and on withdrawal? Explain. c. Set the other bottle mouth upwards on the table and leave it open for one minute. Then bring a hghted taper to the mouth (?). Explain. d. Fill a test-tube over water with the gas. Bring this tube, mouth downwards, mouth to mouth with a test-tube filled with air, and keep them in this position for 3 minutes. Then apply a light first to the lower (?) and then to the upper tube (?). What fact about the molecules of gases is shown by this experiment? e. Record the observed physical properties of hydrogen, namely: color (?), odor (?), density compared with air (?); also any chemi- cal properties observed (?). f. (Optional.) Another Method of Obtaining Hydrogen. Fit a test-tube with a one-hole cork and dehvery tube (Fig. 5). Pul- verize about 2 g. of sodium hydroxide, mix it intimately in the mortar with about 3 g. of zinc dust, and place the mixture in the test-tube. Insert the cork and delivery tube, test the apparatus for air-tightness, Exercise 3 d, and clamp the tube in a horizontal po.sition (why?). Heat the mixture and collect the gas (?) over water (Fig. 14) in a test-tube. If the tube should crack [Caution] cease heating at once. To learn whether the gas is combustible, when the test-tube is full of the gas, close the mouth with the thumb and carry the tube, mouth downward, to a flame (?). Assuming that the residue in the tube is sodium zincate [576], write a balanced equation for the reaction. EXERCISE 16 Valence of a Metal by Displacement Object: To determine: (1) the weight of hydrogen which is displaced by one at. wt. (24.3 g.) of magnesium, and (2) the valence of magnesium. If, for example, 24.3 g. of magnesium is found to displace (and combine in place of) one at. wt. (1 g.) of hydrogen, then magnesium is univalent. If it displaces two at. wts. of hydrogen (2 g.), it is bivalent, and so forth (quantitative). Apparatus : Balance. 250 c.c. bottle. Trough (stone- ware or enameled). 50 c.c. graduated cylinder. Glass plate. Thermometer. Barometer. Materials: Magnesium ribbon. Hydrochloric acid (cone). a. Weigh (balance) to the nearest centigram exactly 2 meters of magnesium ribbon (?). Calculate what length will weigh exactly 0.2 g. and cut off this length for use. (These strips may be cut previously by instructor or assistant to save time.) Record all data as shown under d. Roll the ribbon into a spiral coil somewhat smaller than the inside diameter of the mouth of the 250 c.c. bottle. Place in the trough about 5 cm. depth of water. Measure into the bottle 30 c.c. of hydrochloric acid (cone), and fill it up to the brim with water. Cover it with a glass plate and invert it in the trough, leaving the glass plate in the trough with the bottle inverted upon it. If any air gets into the bottle, lift out the bottle with the plate firmly pressed against the mouth, fill it up with water and try again. Wash your nands immediately, if you have to immerse them in the dilute acid at any stage of the ex- periment. Place the spiral of magnesium ribbon in the trough and slip the mouth of the bottle over it, setting the bottle down firmly on the bottom of the trough. Now tilt the bottle as little as possible, and slide a piece of thin copper wire under one rim (*^). b. When the magnesium has all disappeared and evolution of hydrogen has ceased, adjust the bottle in the trough (adding water, if necessary) until, on looking horizontally, with the eye at the level of the water, the levels inside and outside are seen to^ 35 36 VALENCE OF A METAL BY DLSPLACEMEXT be ihf -a.ii<'. Incline the bottle, if necesftary, to accomplish this. WTiile the bottle is in this position, cover the mouth with a glass plate (or insert a cork), and set the bottle with its contents mouth upwards upon the table. Read the temperature of the water (?). Ascertain also the height of the barometer (?). If there is not time to proceed with the operations directed below, the bottle and its contents may be set aside until the following period. c. The weight of this hydrogen is to be found, not by weigh- ing it directly, but by measuring its volume, and using the fact that 22.4 liters of the dr>' hydrogen at 0* and 760 mm. weigh 2g. (iiee d) . cL Use a ^duated cj'linder (500 c.c.j to fill the bottle once more to the top with water, noting carefully the volume of water required (?). The hydrogen was mixed ^^-ith water vapor. Find the tension of the aqueous vapor at the temperature recorded in a [Appendix I] (?) and subtract this from the barometric height (?). Reduce the volume of hydrogen, from the observed tempera- ture and barometric pressure as just corrected, to 0° and 760 mm. (?). Calculate the weight of this hydrogen. 22.4 liters weigh 2 g. Weight of metal taken g- Volume of hydrogen obtained c.c. Temperature e Barometric height mm. Tension of aqueous vapor mm. Pressure of hydrogen, corrected mm. Volume of hydrogf-n at 0'' and 760 mm , c.c. Weight of this hydrogen g- The atomic weight of magnesium I is 24.3. State just what experimental fact this sentence represents (?). f. The weight of hyrlrogen found in d was that dispaced by the weight of magnesium taken in a. Calculate from these data the weight of hydrogen which would be displaced by one atomic weight r24.3 g.) of magnesium (?). What is the nearest whole VALENCE OF A METAL BY DLSPLACExMEXT 37 number of atomic weights of hj^drogen (1 g.) contained in this weight of hydrogen? This whole number is the valence of mag- nesium. Mg therefore displaces xH. Supply the value you have found for x (?). g. How many formula weights of hydrochloric acid (HCl) are required to furnish this amount of hydrogen? Now make the complete equation, supplying the values you have found for X, y and z: Mg + 2/HCl->Mga + ia:H2. Why do you write ^a:H2 in this equation, rather than xH? You did not measure the weight of Clz, or determine the value of z. What law of chemistry enables you to supply this value without measurement? h. Some members of the class may be instructed to use alumin- ium wire, following otherwise all the directions given for magne- sium. The final results obtained from the two metals should be contrasted and explained in the class-room. EXERCISE 17 Water — Physical Properties Object: To learn how to purify water, ami how to find out whetlier it contains non-volatile impurities. Apparatus: Flask. Glass tubing. Test-tubes. Beakers. Clamp. Ring stand. Wire gauze. Watch-glass. Materials: Marble (chips). Potassium permanganate Csol.). Phenolphthal- ein (sol. in alcohol, 1 : 500). Ammonium hydroxide (sol.). a. Put on a clean watch-glass 3-4 drops of distilled water, place the watch-glass on a 100 c.c. beaker half filled with water, and set the beaker on the wire gauze and boil (see directions in Exercise 14 b). Put on a second clean watch-glass 3-4 drops of tap-water and evaporate in the same way. Compare the two watch-glasses when dry (?). Do the specimens of water contain any non-volatile impurities? b. Distillation. Bend a 30 cm. piece of glass tubing twice at right angles (see Fig. 17) and fire-polish the ends. Connect with it, by means of a short piece of rubl>er tubing, a second glass tube also about 30 cm. long. Set up a flask and a test-tube immersed in cold water in a large beaker as in Fig. 17. Place in the flask about 100 c.c. of water, some marble chips (to prevent " bump- ing"), artd a few 'drops of potassium permanganate solution. Boil the water and examine the distillate (in the test- tube). In what way has the water been Fig. 17. purified by the distillation? Is pota.s- sium permanganate volatile under these conditions? If it had been, would distillation have purified the water? C. Add one drop of phenolphtlialcin solution to some taj)- 38 I WATER — PHYSICAL PROPERTIES 39 water (?). Add one drop of ammonium hydroxide solution to some tap-water, and then add one drop of phenolphthalein (?). d. Using a glass rod, add a single drop of ammonium hydroxide solution to 100 c.c. of tap-water. Clean and use the same appa- ratus as in b, place this water in the flask, and distill as before. In each of six clean test-tubes place, from a glass rod, one drop of phenolphthalein solution, and use these test-tubes one after another to catch the distillate. Change the test-tube when 10 c.c. of liquid has come over until the six have been used. While changing, remove the flame and uncork the flask each time. If the water in the beaker becomes warm, change it for cold water. What evidence is there that ammonia passes over with the steam? Which portion of the distillate contained the most am- monia and which the least? Cool the residue in the flask in run- ning water, pour 10 c.c. of it into a clean test-tube and add one droD of phenolphthalein (?). Can water be purified from a volatile impurity? It should be noted that glass of poor quality is appreciably soluble in boiling water, and the resultant solution gives a reaction with phenolphthalein [526]. It is not probable, however, that this complication will cause you to obtain a positive test with your residue on addition of the indicator. Any decided coloration is much more likely to be due to your adding far too large a quantity of ammonium hydroxide at the start. The action of water on glass, nevertheless, may be made evident in a very short time by increasing the surface. Take a Uttle glass wool in a test-tube, shake up with distilled water, and test with phenolphthalein. 'VMiat do you observe? e. Devise two methods for purifying water from clay sus- pended in it, and submit to your instructor for approval. Which would be the easier method of purification for water containing clay as an impurity? Would this method apply if salt were also present? EXERCISE 18 Hydrates Object: To learn how to find out whether a substance is a hydrate or not Apparatus: Watch-glass. Test-tubes. Clamp. Mortar. Materials: Washing soda. Potassium chlorate. Aluminium sulphate. Potassium sulphate. Barium chloride. Gypsum (fragments). Cupric sulphate (blue vitriol). Cobalt chloride (sol.). a. Place a clear crystal of washing soda (sodium carbonate) on a watch-glass and set it aside. At the beginning of the next laboratory period, examine it and record any changes you ob- serve (?). b. Place a clear crystal of washing soda in a dry test-tube and heat the crystal gently (?). What condenses on the walls of the tube? Explain the result of a [154]. c. Place in different dry test-tubes about 1 c.c. each of potas- sium chlorate, aluminium sulphate, potassium sulphate, barium chloride, and gypsum (calcium sulphate). Clamp one tube in a horizontal position, to prevent any condensed water from run- ning back and causing the tube to crack, and heat the substance in it with the tip of a small flame until no further change occurs (?). Repeat with each tube. Record the results in tabular form as follows: Substance What Amount of V. Appearance Substance was Heated Change Condensed OF Final A Hydrate Water Rp:sidue OR NOT The amount of the water condensed may be '' great," *' small," or '' a trace. " Do not, however, let the appearance of a trace of mois- ture deceive you into reporting a hydrate. Even an empty '' dry " test-tube will show a slight film of condensed vapor on its cooler part, when heated in the flame. Every powder which has been exposed to the air at all will give some moisture (see Exercise 11 d and adsorpfioti [487]). You must, therefore, })efore recording 40 1 HYDRATES 41 any result, decide whether the amount of water obtained is sig- nificant. Are all crystalline substances hydrates? Illustrate. Write an equation for the change in each case in which water was given off. d. Take about 1 c.c. of copper sulphate (blue-stone) crystals. Note their color (?). Pulverize them finely in the mortar and note the color again (?). Explain. Place the powder in a dry test-tube, clamp the latter in a hori- zontal position, heat the substance as in c and tabulate the results as before. Leave the tube in the clamp until it is cold, and then set it upright (?). If there is not enough water condensed to permit some to run down to the solid residue, add two drops (?). Note the color. What substance is formed? Feel the bottom of the test-tube. What evidence is there of a chemical change? Write an equation, showing the action to be reversible [154]. Record its color under the formula of each substance. e. Take a clean match and, after dipping it in a solution of cobalt chloride, write upon a piece of white paper. After the writ- ing is dry, warm the paper gently by waving it above a Bunsen flame (?). Now, breathe repeatedly upon the writing (?). Write equations for the actions that have occurred [613]. f. Hydroxides. (Optional.) Place a pinch of cupric oxide in a test-tube and wash it by shaking with a little distilled water and pouring off the liquid. Add more water and shake again. Test this latter solution with litmus paper (?). At the same time test a sample of the water with litmus paper and compare the tints. Repeat with calcium oxide (?), barium oxide (?), sulphur dioxide (?), phosphorus pentoxide (?), and carbon dioxide (?) (refer to Exercise 12). Some oxides do not interact readily with water (which?) . These oxides which do interact may be divided, according to the natures of the products they give, into two classes. What are those classes, and which oxides belono^ to each? What are the two classes of elements whose oxides belong to the two groups, respec- tively [151-2]? EXERCISE 19 Quantitative Measurement of Water of Hydration Object: To find the per cent of water of hydration in gypsum (hydrated calcium sulphate) or in barium chloride crystals. Apparatus: Porcelain crucible. Balance. Pipe-stem triangle. Materials: Gypsum (powdered crystals). Barium chloride (crystals). a. Clean and dry the porcelain crucible and weigh it to the nearest centigram (0.01 g.). Then place in it about 2 g. of pul- verized gypsum (do not try to take this exact amount) and weigh again as before. Record the weights in tabular form as shown below. Support the crucible (open) on the pipe-stem triangle, placed on the ring of the iron stand (Fig. 12, Exercise 7), so that the bottom of the crucible is a short distance above the inner cone of the Bunsen flame. Lower the flame and heat at first very gently to avoid loss of any particles by sudden splitting of the crystals. Later use the full flame. After 15 minutes' heating, allow the crucible to cool and weigh to the nearest centigram. Replace the crucible on the triangle, heat again for 5 minutes, allow to cool and weigh again. If the weight is less than before, heat once more, and repeat until two successive weighings are identical, i.e., "heat to constant weight." Wt. of crucible + gypsum g. Wt. of crucible empty "" g. Wt. of gypsum taken g. Wt. of crucible + gypsum g. Wt. after last heating g. Wt. of water of hydration g. wt. of water X 100 ^ Per cent of water = wt. of gypsum When the percentages obtained })y all who have done tne ex- periment are compared, what law of chemistry is found to be 42 WATER OF HYDRATION 43 illustrated? Record the average of the values found by all for the percentage. b. Some members of the class may be directed to use barium chloride crystals, following otherwise all the directions given for gypsum. c. From the data obtained in a or b, calculate the formula of the hydrate used. Proceed as follows: Wt. of water -^ Formula wt. = x. (H2O = 18) Wt. of residue -r- Formula wt. = y. (CaS04 = 136) Wt. of water _ 18 X a: _ ^(HgO) Wt. of calcium sulphate 136 X y ?/(CaS04) ' Divide both x and y by y (the smaller factor). This will give (within experimental error) the smallest whole numbers which are in the same ratio. Then substitute these whole numbers for x and y in ?/CaS04,xH20. In b, the formula is ?/BaCl2,xH20, and the values of x and y are found in the same way. EXERCISE 20 Atomic and Molecular Weights Object: To find atomic weights from data given. Also to become familiar with the relations between density and molecidar weight. a. From the data obtained in Exercise 13, calculate the weight at 0° and 760 mm. of 22.4 liters (the molecular weight) of oxygen. Compare the molecular weight found with the atomic weight of oxygen (?). How many atoms of oxygen are there in one mole- cule of the element? b. The weights of one G.M.V. (22.4 liters at 0° and 760 mm.) of several compounds of carbon are as follows: For- mula Carbon monoxide Carbon dioxide. . Methane Ethylene Glycerine (vapor) Weight Weight Weiglit Weight 22.4 1. carbon hydrog<>n oxygen 28.00 12.0 16 44.00 12.0 32 16.032 12.0 4.032 28.032 24.0 4 032 92.004 3G.0 8.004 48 What value should you select for the atomic weight of carbon [167]? Assuming the atomic weights to be, for hydrogen H = 1.008, for oxygen O = 16, and for carbon C = ?, WTite the for- muliE for each of the five compounds. c. The density (wt. of 1 c.c. at 0° and 760 mm.) of ethylene chloride is 0.00433 g., what is the molecular weiglit [163]'.' d. Using the weights in 22.4 1. given above, find the weight of 1 c.c. (the densities) of methane and carbon dioxide. e. How do the densities of the five substances mentioned in b comparo with that of air [220)? f. The weight of zinc combining with 3').4() g. (one atomic; weight) of chlorine is 32.68 g. The specific h(^:it of zinc (metal) is 0.0936. What is the atomic weight of zinc [174]? 44 EXERCISE 21 Solvents and Solubility (With practical applications) Object: To find out how to hasten the process of solution, and the difference between solution and suspension. To learn what solvents dissolve certain common materials. Apparatus: Test-tubes and rack. Corks to fit. IVIortar. Graduated cyl- inder. Glass rod. Separatory funnel. Watch-glass. Materials: Cupric sulphate (blue-stone"). Filter-paper. Powdered rosin. Alcohol (95% denatured). Fat (or lard). Carbon tetrachloride. Par- affin. Gasoline (or benzene). Ether. a. Take two large crj^stals of cupric sulphate of equal size and yet of such size that each can be slipped into a test-tube. Pro- vide two dry test-tubes with corks to fit. Pulverize one of the crystals very finely in the mortar so that no large particles are visible. Place the powder in one test-tube and the crystal in the other. Add from the graduated cylinder 20 c.c. of water to each. Cork the tubes quickly, note the time on a watch (?), and shake the tubes gently. When the powder has all dissolved, note the time again (?). Estimate the fraction of the original crystal which remains in the other tube, then continue shaking it until it also has dissolved, and note the time again (?). Compare the total times required to dissolve each (?). Why does pulverization make this difference in the rate of solution? To save time, in what form should you use a substance to be dissolved? b. Take again two nearl}^ equal-sized, but much smaller crystals of cupric sulphate. Fill two test- tubes with water. Put one of the crystals into one of the tubes. Why does it fall to the bottom? Place the other crystal in the second tube (Fig. 18), so that it rests on a narrow strip of ordinary paper and is only just covered by the water. Set both tubes upright in the rack. How long does each crystal take to dissolve? Explain the difference in time. If you had to dissolve a large amount of material quickly, 4o Fig. is. 46 aOLVXNTS ASD SOUIBILITy with tibe leaHt eaqieiiditaie of df ort, horn AatM yoa piDCced ^ Mtswamg, take the icsnlts of both m and b into account)? While the tubes aic aAgmding, gp on with c» d and e> c Place 1 ex, ol powdeied nnn in each of two dij tcat-lnb^ Add to one 5 ex, of alcohc^ and to the other 5 ex, of water and riake both (?), Poor the alcoholic fiqnid into a kiB? beaker foD of water and rtir(?), Inwhat wa^kaia^eDaonlikeaioiaticm (?) and how docs it differ? Goold jou lemore losn (;or vainidi or a f?— flflr gnm) from dothine; with water? IHthalccrfiol? dL Place a anall piece cif lardf half the aae of a pea, in each of two tc^-tobe^ Add 2 ex^ of water to one and 2 ex, of caibon tetiadilofide to the other and diake (?), How eoold yon ic^ move giease from ck«hing? (In rnnoiins a grease-spot, place the part flat on a piece of blotting paper, to absorb the soiirtion, and mb the spot with a rag dipped in the solvent,) e. Use amall pieces of solid paraflfai as in d, employing water and gaiwiine or benaene as solrents, t Take 10 ex, of water in each of three tci^4nbes. To one add a angje drop of alcohol and diake. Does the alcohol dis- solve? Add moie alcohol a few drops at a time until aboot 5 ex: have been added, Has the anwwnt added j^ b^cwnc greater than the water can disK^hre^ To the second tnbe add earrx^>ii netriohlor:: • ... ...... -^- - i.y. (or benaene) in fehc same way, and ai»wer th*^ -.:...• ..•-*.. r..- H joo had a mixtore of sugar and fat en a pwce ot cio^h, bow coold yotr r^mo^ff firft one and tli^ tfw othw frimriytnrent nf thp nuxtoT'^ separator/ fiinnei * Af^^r i ^' ■ carefully ran off, A and a fisf' ' :' ' sulphate Cprepared as m Exf^rci."^: 18 d; co a What dr. :' :-<^* Flxplam hri^ny EXERCISE 22 Solubility and Temperature. Saturation Object: To learn how to make a saturated solution, and to know approximately the amount dissolved (approx. solubility). Also to study the influence of temperature on solubility. Apparatus: Test-tubes. Funnel. Watch-glass. 100 c.c. beaker. Trip scales. Materials: Calcium sulphate (powdered). Calcium carbonate. Filter- paper. Potassium dichromate (cryst.). a. Test of Degree of Solubility. Place 1 c.c. of powdered cal- cium sulphate in a test-tube and shake with 10 c.c. of water for two or three minutes. Filter the mixture, catching the clear fil- trate in a clean test-tube. Treat as in Exercise 17 a to see whether any dissolved (?). Examine 1 c.c. of powdered calcium car- bonate (chalk) in the same way (?). Compare the deposits on the watch-glasses (?). Which substance is more soluble? What conclusion should you have drawn from mere shaking with water without completing the test? Was the solution you evaporated saturated? Was it con- centrated? What is a saturated solution? On what factors does the amount of a substance that will go into solution depend? How is the solubility usually expressed? b. Pulverize 6 g. of potassium dichromate. Describe the change in color and explain it (?). Shake the powder with 10 c.c. of water in a test-tube until the liquid is saturated. What evidence is there that a good deal dissolves? Now warm the contents of the test-tube gently, with occa- sional shaking (?). Is the substance more or less soluble as the temperature rises? When all has dissolved set the tube in the rack and examine it when it has cooled (?). Describe the contents. Warm the contents of the tube carefully (to avoid cracking the tube) once more until all has dissolved. Then hold the tube in running water to cool it rapidly (?). Describe the contents (?). Note two differences (in size of particles and in color) between the results of slow and of rapid cooling and explain each (?) . 47 EXERCISE 23 Hydrogen Chloride — Preparation and Properties Object: To obtain hydrogen chloride and to learn some of its properties, both in the gaseous state and in aqueous solution. Apparatus: Test-tubes. Glass rod. Watch-glass. Lens (one for class). Materials: Ammonium chloride. Calcium chloride. Potassium chloride. Sulphuric acid (cone). Litmus paper. Ammonium hydroxide (sol.). Sodium chloride. Silver nitrate (sol.). Zinc (dust). Sodium-hydrogen sulphate (saturated sol.). a. Place a few small crystals of each of the following chlorides (ammonium chloride NH4CI, calcium chloride CaCU, and potas- sium chloride KCl) in separate test-tubes and add a few drops of concentrated sulphuric acid to each (?). Is the material boiling (feel the bottom of the tube; sulphuric acid boils above 300°)? What word should be used to indicate the evolution of a gas from a liquid that is not boiling? Waft a little of the gas towards the nose, but do not bring the latter too near to the tube (odor)? To learn the behavior of the gas with water vapor, blow the breath across the mouth of one of the tubes (?). Moisten pieces of blue and of red litmus paper with water (to dissolve the gas) and place them in the mouth of one of the test- tubes (?). What chenu'cal property does the result show the aqueous solution of the gas to possess? Dip a glass rod in ammonium hydroxide solution. Smell the rod (?). The gas which is dissolved in, and given off by this solution is amrtionia (NH3). Now insert the glass rod into the mouth of one of the test-tubes (?). The product is formed from the ammonia gas and the hydrogen chloride gas. Light a wooden splint and plunge the flame into the test-tube (?). Does the gas burn or support condnistion? Four properties of hydrogen chloride (or its solution) have been observed. Make a list of these, and note opposite each whether it is a physical or a chemical property. 48 L HYDROGEN CHLORIDE — PREPARATION AND PROPERTIES 49 b. Of what elements is hydrogen chloride composed? What is its formula? What proportions by weight of the constituents are indicated by this formula? Write the equations for the original actions by which, in a, you obtained the gas. Note that the three chlorides suggested will give, respectively, (NH4)HS04, CaS04, and KHSO4, as one of the products. Where is this one of the products? To which of the varieties of chemical change do these actions belong [203?] c. Write the equation for the interaction of ammonia and hydrogen chloride. To which of the four varieties of chemical change does this action belong? d. Take a few small crystals of sodium chloride in a dry test- tube and add a few drops of concentrated sulphuric acid. Place in a second test-tube 0.5 c.c. of silver nitrate solution. Dip a clean glass rod in water and hold the rod with the adher- ing water in the gas issuing from the first test-tube for one minute. Then transfer the rod, with the adhering solution, to the liquid in the second test-tube (?) . To obtain a better idea of this action, add to the same silver nitrate solution one drop of concentrated hydrochloric acid (?). Write the equation. e. Place on the watch-glass a few particles of zinc dust. Dip a glass rod in water, hold it in the hydrogen chloride as in d, and then place the drop of the aqueous solution of the gas on the zinc dust (?). What is the gas liberated (see Exercise 14 d)? Make the equation for this action (?). Name three other metals which would react in a similar way with hydrogen chloride solu- tion (?). Write equations for these three actions (?). f. Make the equation for the action in par. 1 of d, and write the name of the substance under each formula (?). Take 5 c.c. of saturated sodium-hydrogen sulphate solution. Add to it concentrated hydrochloric acid, a very little at a time, shaking the mixture after each addition (?). Examine the pre- cipitate with a lens and describe the form of the particles (?). Make the equation for this action (?). Compare the two equations last written. What substance, by its escape as a gas from the mixture, permitted the first action to .50 hvdiuk;en chloride — preparatk^x and properti&s go to completion? If this substance had remained dissolved, what difference would this have made in the result? What substance, by its separation as a precipitate, permitted the second action to go to completion? Explain why the separation of a product per- mits the completion of a reaction [197-9]. g. (Optional.) Preparation of a Chloride. I^ad chloride may \)e prepared by following the directions given in Exercise 81, a, b, and c. As an alternative, cuprous chloride may be prepared as follows : Take 50 c.c. of concentrated hydrochloric acid and dilute it with an equal volume of water. Warm with 4 g. of cupric oxide in a flask until all the cupric oxide is dissolved. Write the equa- tion for this reaction. Now add to the dark green solution about 10 g. of clean copper turnings, and continue to warm the solution (do not boil!) until it becomes clear and colorless [589]. While the solution is still quite warm, pfjur it into a beaker containing 4(X) c.c. of cold water (?). Allow the precipitate to settle and decant off as much of the liquid above it as possible. Filter, and wash thoroughly, first with water containing a little hydrochloric acid, then with alcohol, and finally with dr>' ether. Is cuprous chloride stable when exposed to air? Which is the more rapidly oxidized, the dry or the moist salt? c EXERCISE 24 Sodium Hydroxide Object: To learn some of the properties of an aqueous solution of sodium hy- droride. Apparatus : Test-tubes. Glass rod. Materials: Sodium hydroxide (sol.). Litmus papers. Cupric sulphate (sol.). Aluminium sulphate (sol.). Phenolphthalein (sol.). Ammonium hydroxide (sol.). a. Recall the action of sodium on water [112] as seen in the class-room. Write the equation for this action, and place the name of the substance under each formula (?). To which of the four varieties of chemical change [203] does this action belong? b. Take 1 c.c. of sodium h^'droxide solution {2N) and dilute it with 10 c.c. of water. Dip a clean glass rod in the diluted hquid and taste it [Immediately rinse the mouth out with water. Taste substances only when told to do so] (?). Dip red and blue litmus paper in the solution (?). Rub the liquid between the fingers (?). Use the same solution in c. c. To 1 c.c. of cupric sulphate solution add one-third of the diluted sodium hydroxide solution (?). [Make the equation and attach to each formula the name of the substance (?). To which variety of chemical change does this reaction belong? Where is the other product of the reaction and how should you proceed so as to separate the precipitate and finally obtain the other product in solid form? d. To 1 c.c. of aluminium sulphate solution add a few drops (shake between drops) of the sodium hydroxide solution (?). Make the equation and answer the same questions (?). e. To the rest of the sodium hydroxide solution add one drop of phenolphthalein solution (?). Litmus and phenolphthalein are called indicators. How does each behave with a base [205 6]? 51 52 SODIUM HYDROXIDE f. What substance have we previously found to have the same effect on phenolphthalein as has sodium hydroxide (Exercise 17 c)? What is its formula [406]? Dilute 1 c.c. of ammonium hydroxide solution with 10 c.c. of water and try with it the tests in b and d (?). g. (Optional.) Titration. See Exercise 31, p. 64. fk lis:: lDmi#L. iw^Mii iirt*rn-^ H L Iwonaraui] ufflp aoiid iRnnr. jjmnt- lifif r "" : -'Hiinf: asnaasi iin tfte rr m^ IllttlirtilWIi lljJMIII - itlBdtaK d^L iij nttff 54 CHLORINE — PREPARATION AND PROPERTIES c. What did you observe that showed chlorine not to be Hghter than air? What other physical properties and what chemical properties were observed? Write the equations for the reactions that occur in a and b. d. (Optional.) Prepare some strips of filter paper by dipping them in starch emulsion to which you have added one drop of potassium iodide solution [215-6]. Place small quantities of finely powdered manganese dioxide, potassium chlorate, lead dioxide, and pure litharge [618] in as many test-tubes, and add a little concentrated hydrochloric acid to each. Notice the color (?) and odor (?) of the gas in each case. If no action takes place in the cold, apply heat. Dip into the gas in one of the test-tubes a strip of the prepared paper (?). How do you account for the difference in the behavior of the two oxides of lead? Do all compounds containing oxygen give free chlorine in this way? If not, state what is common to those which do and to those which do not (?). EXERCISE 26 Chemical Equilibrium Object: To study a reversible action, to show that it is incomplete, and to try one of the ways of carrying such a reaction to completion. To demonstrate the incompleteness of some apparently complete reactions. Apparatus: Test-tubes. Hydrogen sulphide generator (Instructor; see Ex- ercise 39 a) . Funnel. Materials: Ammonium thiocyanate. Ferric chloride. Lead nitrate (sol.). Hydrochloric acid (dil.). Calcium chloride (sol.). Sulphuric acid (dil.). Barium chloride (sol.). a. Place 10 c.c. of water in each of two test-tubes, add to one a single drop of ammonium thiocyanate solution, and to the other a single drop of ferric chloride solution. Now mix the solutions (?). The radicals are (NH4)(CNS) and (Fe)i" (01)^3. Write the equation for the action which may be assumed to have occurred. Is there any evidence that interaction has taken place? Which of the four is the colored substance? Use the mixture for b. b. When no precipitate is formed, is an action like the above complete? To answer this question, divide the mixture from a equally between four test-tubes. Keep one for reference. To the second add one drop of ferric chloride solution (?), and to the third a drop of ammonium thiocyanate solution (?), In- terpret the result. Now add to the fourth tube a few drops of ammonium chloride solution (?) and explain. What other action have we shown to be reversible (Exercise 23 f)? All double decompositions of acids, bases and salts in solution are reversible, like these two. They are also often far from complete, when, as in the present instance, precipitation does not occur. Why does precipitation tend to make the action more nearly complete? c. To a few drops of a dilute solution of lead nitrate, in a test- tube, dilute hydrochloric acid is added in excess. What do you observe? Write the equation for the reaction. Heat the test- 55 56 CHEMICAL EQUILIBRIUM tube carefully with a small Bunsen flame (?) until the solution is almost at the boiling-point (?). What makes the reaction more complete at low temperatures than at high? Cool the contents of the test-tube rapidly by holding the tube under the cold water tap (?). Continue until all solid precipitating out has settled to the bottom of the tube and the supernatant liquid is quite clear. Decant some of this liquid carefully into a second test-tube (if impossible to separate from traces of precipitate, filter!) and bubble hydrogen sulphide gas H2S through it for a few seconds. What do you observe now? Write the equation for this second reaction. Which of the two reactions is more nearly complete? Devise a simple experimental method of confirming quantitatively the fact that your answer is correct (Hint: Read Exercise 17 a.) d. To a few drops of dilute sulphuric acid, in a test-tub(% cal- cium chloride solution is added in excess. What do you observe? Write the equation for the reaction. Filter the solution and add a few drops of barium chloride solution to the filtrate. Continue the question as in the last four lines of c above. e. (Optional.) Properties of Solutions: Volume Changes and Thermal Effects. Take about 25 g. of potassium carbonate and determine its weight to the nearest tenth of a gram. Assuming the specific gravity to be 2, calculate the volume you have taken (?). Place in the graduated cylinder exactly 85 c.c. of water and ' take its temperature. What is the sum of the volumes of the water and the carbonate, separately? Add the potassium car- bonate to the water, dissolve by repeated inversion of the cylinder, closing the mouth of the latter with the hand, and read the volume of the solution (?). Read also t|je temperature of the solution immediately (?). What relation exists between the sign of the thermal effect when a substance is dissolved in a nearly saturated solution of the same substance, aiul the cliange of solubility with temperature [246-7]? What do you infer in this case? Repeat, using about 25 g. of ammonium chloride (sj). gr. 1.5). Make the same observations and answer the same questions. EXERCISE 27 Displacement Object : To establish the order of activity of zinc and copper. Apparatus: Beaker. Test-tubes. Funnel. Materials: Zinc (granulated). Cupric sulphate (sol.). Zinc sulphate (sol.). Ammonium sulphide (sol.). a. Place several pieces of granulated zinc in a dilute solution of cupric sulphate and set aside until the change is complete (test?). Occasional agitation will hasten the change (why?). Filter. What is the precipitate [254]? Preserve the filtrate. Before examining the filtrate take a few drops of cupric sul- phate solution and a like amount of zinc sulphate solution in two test-tubes. Dilute each solution with water and add to each ammonium sulphide solution (?). What is the precipitate in each case [328], and what ions are required to form it? b. To the filtrate from a add ammonium sulphide solution (?). What ions were present in the filtrate? What changes did the metallic zinc and the cupric ions, respectively, undergo in a? For- mulate these changes in an equation. What substances could have been substituted for the cupric sulphate without affecting the result so far as the consumption of zinc and the precipitation of copper were concerned? What substances, besides zinc, would have precipitated copper [269]? What other elements, besides copper, are displaced by zinc? c. Which one of the elements displaced by zinc did we prepare in quantity by an action like the present (Exercise 15)? Formu- late this action in terms of ions. What is the significance of the fact that the acid employed in this action was considerably diluted with water? What are the products of the action of zinc upon concentrated sulphuric acid (Exercise 14 e)? Explain [259-60]. 57 EXERCISE 28 Double Decomposition Object: To study some typical double decompositions between electrolytes in solution. Apparatus: Test-tubes. Funnel. Watch-glass. Bunsen burner. Materials: Silver nitrate (sol.). Potassium chloride (sol.). Calcium chlo- ride (sol.). Sodium hydroxide (sol.). Cupric sulphate (sol.). Hydro- chloric acid (dil.). a. Precipitation. Place 3-4 c.c. of silver nitrate solution in a test-tube and dilute with water. Add potassium chloride solu- tion cautiously and agitate continuously, until no further pre- cipitation occurs (?). Filter, concentrate the filtrate by evapora- tion, and pour it into a watch-glass to crystallize (?). Formulate the action (as shown below). Kci ^ K+ -f cr AgNOs ^ NO3" + Ag+ Ti U KNO3 AgCl (dissolved) Ti AgCl (solid) Upon what factor does the completeness of the change depend? Is, or is not, silver chloride a highly ionized substance [257]? Aside from double decompositions, what means have we for learning of what radicals a salt (like silver nitrate) is composed? b. To a little calcium chloride^fiolution in a test-tube add sodium hydroxide solution (?). Exactly, as in a (second par.), formulate and explain the whole action. To what classes of electrolytes do the four compounds involved in this formulation fepectively belong? c. To a little cupric sulphate solution add a little dilute hydro- chloric acid (?). In what n^spects does the result differ from thosci in a and b, and why? In future, formulate all double decompositions between electro- lytes in the way indicated in a. 58 I EXERCISE 29 Ionization of Acids, Bases, and Salts* Object : To compare the extents of ionization of various acids, bases and salts. Apparatus: Electrolytic cell and electrodes. Storage batteries or lamp- board (Instructor). Materials: Sodium chloride (0.1 A^ solution). Sodium hydroxide (0.1 N sol.). Hydrochloric acid (0.1 N sol.). Ammonium hydroxide (0.1 A^ sol.). Acetic acid (glacial and 0.1 A^ sol.). Ammonium chloride (0.1 N sol.). Ammonium acetate (0.1 A^ sol.). Sugar (0.1 A^ sol.). Toluene. Dry hydrogen chloride. a. Name several distinct methods by which we may ascertain experimentally whether a substance is ionized in solution or not, and may learn the apparent extent of the ionization [271-5] (?). Define the term ionization, first in theoretical terms (?), and second in terms of the experimental evidence (?). Obtain [Storeroom] an electrolytic cellf (Fig. 19). Half fill the cell with the substances named below in turn. See very particularly that the electrodes ^^^' ^^' in the cell are not touching one another. Connect with the termi- nals on the lamp boardj (Fig. 21), and note whether the lamp glows or not (?). The cell is in series with the lamp and, if the lamp glows, the solution is a conductor. If it does not glow, the solu- tion is a non-conductor. Wash the cell and electrodes and wipe the latter very carefully after each trial. * The experiments of this exercise may be postponed until after the work in Exercise 30 or 31 has been done. The apparatus should be set up by the instructor and explained to the class before use. t The cell consists of a glass, flat-bottomed, specimen tube (about 75 X 22 mm.) fitted with a two-hole rubber stopper in which a vertical groove has been cut to permit the escape of gases. The electrodes are pieces of tin about 10 cm. long. I A storage battery of three lead cells or five Edison cells in series ma}- be used, but is always in danger of being ruined by short-circuiting through care- 59 60 IONIZATION OF ACIDS, BASES, AND SALTS The following substances, or solutions, show the behavior typical of various classes of materials. After giving the result in your notes, name the class which is illustrated in each case. If a solution is a conductor, what conclusion is to be drawn in regard to the condition of the dissolved body? In each such case, write an equation showing the materials present in the solu- tion, and write the name under the formula of each substance (?). Pure (glacial) acetic acid (?). Distilled water (?). /, 0.1 N aqueous solution of sodium chloride (?). /^ 0.1 iV aqueous solution of sodium hydroxide (?). A. 0.1 N aqueous solution of hydrogen chloride (?). / 0.1 iV aqueous solution of ammonium hydroxide (?). 0.1 N aqueous solution of acetic acid (?). lessness. Protection by means of a fuse leads to continual interruptions of the work. Where direct current is employed in the lighting system, the best plan is to use the circuit through two resistances of such I/O v-DC ratio to each other as to give the desired potential by the drop over one of them. Thus, if we place a 20-ohm re- sistance and a 3.o-ohm resistance on a 110-volt circuit 80 Wott, Word- Leonard, y^O>>mi tie Alt f Once Fk;. 21. (Fig. 20, diagrammatic), the potential drop over the lower resistance will be about Ki.T) volts. If these re- sistances be of sufficient carrying capacity (say, 5 am- peres), then four different current outlets may be pro- vided — each one with i)lenty of current for one of the electrolytic cells previously described. Each of these outlets is in series with a small battery lamp, used as an indicator of the flow of current through the cell (Fig. 21). Where alternating current only is available, a small rotary transformer, now commonly emjjloyed for chiirging autom()l)ile batteries, may be used. \ I IONIZATION OF ACIDS, BASES, AND SALTS 61 8. 0.1 A'' aqueous solution of ammonium chloride (?). ^ 9. 0. 1 A^ aqueous solution of ammonium acetate (?).^' 10. 0.1 iV aqueous solution of sugar (?). ' Now, dry the cell by- washing first with alcohol and then with ether. 11. Toluene in the dried cell (?)./ \^/ <* 12. Hydrogen chloride dissolved in dry toluene (?). What difference between water and toluene do tests 5 and 12 bring to light? b. Each of four wide glass tubes is fitted up as follows: The lower end is closed tightly with a two-holed rubber stopper, through which pass an electrode and a small tube with stop-cock and nozzle. The upper end is also plugged with a two-holed stopper through which pass loosely a long narrow tube enclosing a second electrode and a funnel for use in filling the tube. The four tubes are fixed upright on a board side by side, and each connected up with a direct-current circuit and a signal lamp (Fig. 20). The tubes are now filled with tenth-normal solutions of (1) hydrochloric acid, (2) acetic acid, (3) sodium hydroxide, and (4) ammonium hy- droxide, respectively. What do you observe when the circuit is completed, the upper electrode remaining near the top of the tube in each case? Explain. What do you observe as the upper electrodes in (2) and (4) are pushed down towards the lower electrodes? Explain. c. One-half of the solution filling each of the tubes in b is with- drawn. The part withdrawn from (3) is added to (1), and the part withdrawn from (4) is added to (2). How is the conductivity of the solution affected in each case? Explain by formulating the reactions in detail. d. Non-Ionic Actions. In previous class-room and laboratory experiments we have observed the formation of electrolytes in other ways than those illustrated in this chapter. Certain of these other ways are non-ionic, or not distinctly ionic. Give illustrations of such of these ways as you recall: acids, two ways, bases, one way; salts, four ways, together with the reference numbers of the laboratory exercises in which they occur (?). EXERCISE 30 Acids and Bases. Neutralization Object: To learn the properties of acids and bases. Apparatus: Test-tubes. File. Porcelain dish. Bunsen. Materials: Litmus (sol.). Phenolphthalein (sol.). Potassium hydroxide. Sulphuric acid (dil.). Sodium hydroxide. Hydrochloric acid. Marble. Iron nail. a. Examine distilled water in respect to (a) taste, (6) behavior with litmus, (c) conductivity (class-room experiment). b. Dissolve a small piece of potassium hydroxide in water and examine the solution in respect to (a) taste, by diluting a little and tasting one drop, (6) behavior with litmus, (c) behavior with phenolphthalein, (d) conductivity (class-room). These properties belong to aqueous solutions of all bases (compare Exercise 24). Aside from the water, what component alone is common to all solutions of bases, and has the above properties? Name this component and give its formula (?). c. Examine a dilute aqueous solution of sulphuric acid in respect to (a) taste, (6) behavior toward litmus, (c) behavior with phenolphthalein, (d) conductivity (class-room), (e) action on a piece of marble, (/) action on an iron nail (clean this with the file before use). These properties are shown to a pronounced degree by all aqueous solutions of strong acids (compare Exercise 23). Aside from the water, what component alone is common to all solutions of acids, and has these properties? Name and give the formula of this component (?). d. Place 3 c.c. of sodium hyaroxide solution in a test-tube. Add about 1 c.c. of concentrated hydrochloric acid. Is there evidence of chemical action (touch the back of the hand with the bottom of the test-tube)? Keep the mixture for e. Make the ordinary [251] and ionic [282] equations for this action, which is a '^ neutralization." 62 NEUTRALIZATION 63 e. Since acids and bases act oppositely on indicators, like litmus and phenolphthalein, it is possible to find out when the propor- tions of the two materials required for complete interaction have been taken, for the mixture will then be without action on an indicator. Dilute the mixture prepared in d. INIoisten a glass rod in it, and touch the edge of a piece of blue and of a piece of red litmus paper with it (?). If the blue turns red, there is excess of acid. Add sodium hydroxide solution a drop at a time, shaking between drops, and moistening the rod and testing as before. Continue until no effect is produced on htmus of either color. If, by acci- dent, too much alkali is added, or if the mixture was alkaline in the beginning, use drops of dilute hydrochloric acid in the same way. When the liquid is neutral to indicators, taste it by touching the tongue with the glass rod (?) . Set the solution aside to evaporate by itself. When it has dried up, examine the solid. What is the form of the crystals? What is the substance? EXERCISE 31 Titration* Object: To learn how to measure the quantity of an acid or of a base contained in a given specimen (quantitative). Apparatus: Burette. Beaker. Glass rod. Materials: Normal acid. Sodium hydroxide (sol.). Phenolphthalein (sol). \'inegar (white). Litmus (sol.). a. A normal solution of any acid is one containing 1 g. of the hydrogen radical (H) per liter, accompanied, of course, by an equivalent amount of the negative radical of that acid. Thus, one liter of normal hydrochloric acid (HCl) will contain 1 + 35.5 g. of the acid. Similarly, a normal solution of a base contains 17 g. of hydroxyl radical (OH) per liter. Thus one liter of normal sodium hydroxide (NaOH) will contain 23 + 17 g. of the base. What weight of acetic acid (H)(C02CH3) is contained in one liter of the normal acid? What weight of potassium hydroxide in one liter of the normal solution of this base? W^hat weight of sulphuric acid II2SO4? What weight of calcium hydroxide Ca(0H)2? b. Titration of a Base with a Standard Acid. Fill a burette with the normal acid. Allow some of the acid to flow out, until all air has been expelled from the ti^ and until the meniscus has reached the graduated portion of the burette. Hold the burette so that the surface of the acid is on the same level with the eye, and read the level of the bottom of the meniscus. Observe that the graduation is downwards, so that a reading two-tenths of a * In the evont of a class threatening to get too far ahead in its Inhoratorv Avork, as compared with lecture work, this exercise may be utilized to fill the gap at any stage between Chapters XII and XIX of the General Chemistry, or at any point after Exercise 22 of this Outline. Before any of the experiments in this exercise are performed, however, the conception of normal solutions [181-2J should be thoroughly explained and grasped. G4 /^. TITRATION 65 c.c. above the 2 c.c. mark is 1.8 c.c. (not 2.2 c.c). Record the reading (?). Take exactly 10 c.c. of sodium hydroxide solution in the gradu- ated cylinder (dry this first). Pour it into a beaker. Rinse out the cylinder three times with a little water (about 5 c.c. each time), and pour each rinsing into the beaker too (?). Set the beaker on a sheet of white paper under the burette, and add a drop or two of phenolphthalein solution (?). Stir vigorously with a thin glass rod. Now allow the acid to run in a rapid succession of drops into the beaker. Stir vigorously after each addition of a few drops. As soon as the acid begins to decolorize the indicator round the point where it enters, proceed more cautiously. Add only one drop at a time, and stir. The aim is to have the solution dis- tinctly pink before the final drop of acid is added, and perfectly colorless when that drop has been allowed to flow in. If, at the first attempt, you overshoot the mark, wash out the beaker, and take a fresh portion of sodium hydroxide solution, read the level of the acid in the burette, and try again. When the titration has been successfully performed, read the level of the acid in the burette (?). Subtract from this reading that recorded at the beginning (?). The difference (?)• is the volume of normal acid required for complete interaction with (neutralization of) 10 c.c. of the solution of the base. c. Since one liter of the normal acid contains 1 g. of available hydrogen, 1 c.c. of the acid contains 0.001 g. of hydrogen radical. Calculate the weight of hydrogen radical used in your experiment (?). How many figures in your result are significant? Neglect all figures, in subsequent calculations, beyond your limit of experi- mental error. Now, 1 g. of hydrogen radical interacts with 17 g. of hydroxyl (OH). Using the weight of hydrogen just found, calculate the weight of hydroxyl contained in the portion of base you took (?). Finally, using the proportion indicated in the formula NaOH, calculate the total weight of sodium hydroxide which contains the weight of hydroxyl you found (?). 66 TITRATION d. Knowing from the result of c the weight of sodium hydroxide in 10 c.c. of the solution, calculate the weight per liter (?). Calculate the concentration of the solution in terms of a normal solution of sodium hydroxide as unity (?). e. Titration of an Acid. Wash out the burette, fill it with the sodium hydroxide solution as in b, and read the level of the me- niscus (?). In c, par. 2, we found the weight of hydroxyl in 10 c.c. of this solution. Calculate the weight in 1 c.c. (?). We may now use this solution containing a known concentration of a base for meas- uring quantities of acids. f. Take exactly 10 c.c. of white vinegar in the graduated cyl- inder (dry this first). Pour it into a beaker, rinse the cylinder three times with water (as in b above), and set the beaker on a piece of white paper under the burette. Add 4 drops of litmus solution, or enough to give the liquid a distinct, but not strong pink color. Stir with a thin glass rod. Now titrate this solution with that in the burette, exactly as described in b (third par.). Aim to stop when the tint is pinkish- violet, halfway between pink and blue. Repeat, if necessary to secure a sharp result. Then read the level of the meniscus (?) and subtract from the former reading to learn the volume of base used (?). g. Using the weight of hydroxyl per c.c. found in e (second par.), calculate the weight of hydroxyl used in f (?). Calculate the weight of acid hydrogen in the 10 c.c. of vinegar Finally, using the fornmla of acetic acid (H)(C02CIT3), calcu- late the total weight of acetic acid in the 10 c.c. of vinegar (?). How much is this per liter? What per cent? Those methods, and others like them, are known as volumetric methods, and are largely used in analyses made for commercial (as well as scientific) purposes. •>: :4r EXERCISE 32 Bromine Object: To liberate bromine, to note its properties, and to try a test for bromides. Apparatus: Test-tubes. Mortar. Materials: Potassium bromide. Sulphuric acid (cone). Manganese di- oxide (powdered) . Carbon disulphide. Bromine- water. Chlorine-water. Caution: Be very careful in all experiments which involve the use or the formation of free bromine. If you are foolish enough to inhale too much of it, give it a gaseous chaser of concentrated ammonia at once (compare Exercise 25). If you spill any upon your hands, wash it off immediately, and cover with a paste of sodium hydrogen carbonate and water (see Note 16, p. xiii). Bromine bums are very painful and exceedingly slow in healing, so do not take any more chances than you can help. a. Take 1 c.c. of water in a test-tube and add slowly 2 c.c. of concentrated sulphuric acid. Pulverize about 0.5 c.c. of potas- sium bromide, add 1 c.c. of manganese dioxide, mix, and add the mixture to the diluted acid.* Warm very gently with a small flame (?). Note the color (?) and odor [Caution] (?) of the vapor. What was the color of the potassium bromide? Does a com- pound show the colors of elements contained in it? Should you expect it to do so? If any of the bromine vapor is condensing on the sides of the tube, describe its properties (?). Write the equation for the reaction [293] (?). b. To 10 c.c. of water in a test-tube add about 2 c.c. of carbon disulphide, close with the thumb, and sh^ke (?). Are the liquids miscible (mutually soluble)? * To this mixture add a few drops of bromine-water [294] (Caution : Do not add more than a few drops and, above all things, * In this experiment, as well as in 33 a, you will not obtain good results unless 3"0U powder your materials finely and mix them intimately. Do not use large lumps. If the experiments are properlj- done, no HBr or HI should appear. r- 68 BROMINE be careful not to add any free bromine that may be undissolved at the bottom of the bottle!) Close the test-tube with the thumlj or with a cork if you prefer, and shake again. Is the bromine, judging by the color, equally soluble in both water and disulphide? If more so in one, how much more (?) and in which? c. Test for a Bromide. Take a crystal of potassium bromide (color?) and dissolve it in 5 c.c. of water (color of solution?). Add 2 c.c. of carbon disulphide and shake (?). Why is the carbon disulphide not colored by the bromine? Holding the tube steady, add now a drop or two of chlorine- water, and observe carefully whether any color appears, and, if so, in which layer of liquid (water layer or carbon disulphide) it makes its appearance (?). Why? Shake vigorously and allow the mixture to settle (?). What substance has been liberated? Write the equation [296] (?). d. Summarize the properties of bromine: color (?), odor (?), density of vapor compared with air (?), relative solubility in water and carbon disulphide (?), relative activity as compared with chlorine (?). EXERCISE 33 Iodine Object: To prepare some iodine and use it to observe the properties of iodine. Also to try a test Jor iodides. Apparatus: Evaporating dish. Mortar. 400 c.c. beaker. Test-tubes. Graduated cylinder. Materials: Sulphuric acid. Potassium iodide (cryst. and sol.). Manganese dioxide (powdered). Alcohol. Carbon disulphide. Splints. Chlorine- water. Bromine-water. Starch suspension. a. Pour into the evaporating dish 1 c.c. of water and add 2 c.c. of concentrated sulphuric acid. Pulverize finely about 1 c.c. of potassium iodide, add 2 c.c. of manganese dioxide, mix, and add the mixture to the acid. Place the evaporating dish upon the ring on the stand and set the beaker with about 50 c.c. of water upon it so that the vapor of the iodine may condense on the bottom of the beaker. Heat the mixture gently with a very small flame, which does not touch the dish. Observe the color of the vapor (?), and the crystals (form?) on the bottom of the beaker. What was the color of the potassium iodide (?), and the form of its crystals? Are its crystals like those of iodine either in form or color? While the crystals are accumulating, proceed with d. b. Place in as many test-tubes 1 c.c. each of water, alcohol, carbon disulphide, and potassium iodide solution. Scrape some of the crystals of iodine oif the bottom of the beaker with a wooden splint, add one crystal to the contents of each of the four test- tubes and shake (?). Is the iodine heavier or lighter than water? Tabulate the results as follows, giving the solvent (?), degree of solubility (slight, considerable, very great), and the color of the solution (look through it at a piece of white paper) : Solvent Solubility Color of Solution Water: Etc.: 70 IODINE The solution in alcohol is the lotion called '' tincture of iodine, '^ That in potassium iodide solution is used in testing for starch (Exercise 56 b). c. Divide the contents of the first test-tube (containing water and iodine) into two parts. To one, add an equal volume of car- bon disulphide and shake (?). Take 15 c.c. of starch suspension (for preparation, see Exercise 66 a) and add the second portion to it (?). Pour the mixture into the graduated cylinder and add water so long as a sample poured out into a test-tube continues to show an easily perceptible color. Why is the use of starch considered to be a delicate test for iodine? Does it show the presence of iodine in combination [299]? d. Test for an Iodide. Take a cry-stal of potassium iodide (color?) and dissolve it in 5 c.c. of water (color of solution?). Add 2 c.c. of carbon disulphide and shake (?). Why is not the color of iodine visible? Holding the tube steady, add now a drop or two of chlorine- water, and observe carefully whether the color appears in the carbon disulphide or in the aqueous layer (?) and what color it is (?). Then shake vigorously and allow the mixture to settle. What substance has been liberated? Write the equation [299]. To what variety of chemical changes does this one belong? e. Repeat d, using bromine-water instead of chlorine-water (?). f. Summarize the properties of iodine: color of solid (?), of vapor (?), density of vapor compared with air and with bromine vapor (?), density of solid compared with water (?), solubihtios in four solvents (?), relative activity as compared with chlorine and bromine (?). Write the equation of the reaction in a, and discuss [213]. i EXEECISE U Comparison- of Htdrogex Haudes Object: To learn how a ddoridey a hramide, on iodide amda, stdpkuric acid, and to obsem Ike imopatiee tf Ae ike halogens. Appantiis: Mortar. Test-tubes. GI&s rod. Leadien dish. C9aaB plate. Materials: Potassiuin cMoride. Soli^mic add (cone.). blue . Ammomuin hydroxide (aoL). Potaasbmi bromide. I\iTnpar(^ Exercise 14 d) f!an yrwi rec- fy^rd2ft by its odor [Caution] " Was thia oriorod^i f^as form^fi ivum r.be poimBsr flolpfeiiric aeid (in an^werini^ eonskier tiie foinmiLi staiu!e« anri of the ga«)? By what sort of cheminai a thw $^ have been formed? Could hydro^n in«! ' pnj- dtu!ed su/!h an action? Wrir.e an er{tiat.ion to y'^'ir- ani^wer (?). Why, then, was irjdine liVierated** g, U.'Jiini? thft r- '^ -• ^> l • ; _. . . a brrimirle and ai. ^liat other method of we Ir ■ -r.'^ h. J. . .-n Fluoride.'' <.ov*r a A<\\xauzft oi' _. : layer of paraffin by warming it very cautiously far air>ove a I: flame and nibbing it on one fi\<]ft wif' ' ' '^ ^ ' about 3 %. of fluorspar in a leaden <; cent rated sulphuric acid (do not cover with the acid). With the end of a file d upon the pri '^ exposing par? rie action of the leaden dish with the j^la^H, paraffin fiiy: down, and set it in mode r)arafi&n m likely ^laaa cover, warm, and wipe off the melted paraffin with filter-paper (T), Write equations representing the act.ion, and state what becomes of each of the constituents of the ^iass f301|. Trv' the teat of rod dipped in ammonium hydroxide and held over the content of the lead dish (?J. r>)es th- .-'^ What autjfttancert, Vjeside fluorsipar, . .• "^'^ '^^ this experiment? Why could noit hydrochloric acid or nitric acid h^ i here for sulphuric t .: itviorine b^ lih)^rar.efi liioride? Why can it not be wfjlated from fluoriries by the oxidizing agents, aH wa« the ca«e with the other halr>gens ; • II dumnd, thia experiment mmy be performrri ny r.np influ-uiiwrf. EXERCISE 35 Hydrogen Peroxide Object: To prepare a solution of hydrogen peroxide, to observe its properties, and to try a delicate test for its presence. Apparatus: Glass rod. Flask. Test-tubes. Funnel. Materials: Sodium peroxide (powdered). Litmus papers. Sulphuric acid (dil.). Manganese dioxide. Splints. Lead nitrate (sol.). Ammonium sulphide (sol.). Filter-paper. Starch suspension. Potassium iodide (sol.). Potassium dichromate (sol.). Ether. a. To prepare a solution of hydrogen peroxide, take 100 c.c. of cold (preferably iced) water in a flask, and about 1 c.c. of pulverized sodium peroxide on a watch glass. Add the peroxide to the water, a very httle at a time, shaking and cooling the mix- ture in running water, or adding ice, during the process. Test a drop of the solution on litmus paper (?). Now, while still shaking and cooling in the same way, add dilute sulphuric acid a few drops at a time, until the mixture is acid. Write the equation (?). What does the solution now contain? b. Take 15-20 c.c. of the solution in a test-tube, and place about 1 c.c. of pulverized manganese dioxide on a piece of paper. Light a wooden splint, throw the manganese dioxide into the solution (?), and test the gas in the tube for oxygen (?). Write the equation (?). The manganese dioxide (catalyst) is un- changed. Is hydrogen peroxide stable or not? c. Take 2 drops of lead nitrate solution Pb(N03)2, dilute with 5 c.c. of water and add 2 drops of ammonium sulphide solution (NH4)2S (?). Pour the mixture on to a filter. The precipitate is lead sulphide, formed by double decomposition. Write the equation (?). Wash the precipitate and whole filter-paper with water and, when the water has run through, wash once more. Then pour upon the precipitate some of the hydrogen peroxide solution [309] (?). Write the equation (?). To what class of sub- 73 74 HYDROGEN PEROXIDE stances does hydrogen peroxide here show itself to belong? What practical use is made of this reaction? d. To a part of the remainder of the hydrogen peroxide solution add some starch suspension (prepared as in Exercise 56 a) contain- ing a drop of potassium iodide solution (?). In writing the equa- tion for this action, remember that the solution of hydrogen perox- ide from a contained a slight excess of dilute sulphuric acid, which will interact with the potassium iodide (?). The product of this action then interacts with the hydrogen peroxide [309]. e. Test for Hydrogen Peroxide. Take about 1 c.c. of potas- sium dichromate solution and, to liberate dichromic acid, add an equal volume of dilute sulphuric acid. Take now the final portion of your hydrogen peroxide solution, add 2-3 c.c. of ether, close with the thumb and shake. Then add to it one drop of the solution containing dichromic acid and shake again (?). The ether is added merely to facilitate the recognition of the colored product formed in this reaction. The color obtained is much more intense and permanent in the ether than in the water layer. f. Summarize the observed properties of hydrogen peroxide, color (?), solubility (?), stability (?), oxidizing or reducing action (?), test (?). EXERCISE 36 Bleaching Powder Object: To find out how the commonest " bleach " does its work, and what kind of substances it bleaches. Apparatus: 90 c.c. generating bottle, 2-hole stopper, thistle. L and delivery tubes. Funnel. Test-tubes. Materials: Bleaching powder. Filter-paper. Marble (chips). Litmus papers. Colored calico (small strips). Hydrochloric acid (dil.). a. Take about 2 c.c. of bleaching powder with 20 c.c. of water in a test-tube, shake from time to time and finalh^ filter to obtain a clear solution. Meanwhile arrange an apparatus to generate carbon dioxide as in Exercise 53 a. (The time of the class may be conveniently saved by the instructor at this point by having a Kipp generator for carbon dioxide set up for general use.) Pour most of the clear bleaching powder solution into another test-tube, reserving a small portion for use in b, and pass carbon dioxide through it for 5 minutes. The precipitate is calcium carbonate CaCOa. Filter again, to obtain a clear solution of hypochlorous acid [312] for use in c. b. In the rest of the bleaching powder solution dip strips of litmus paper. Leave one in the solution (?). Does bleaching powder solution bleach? Hang the other in the air (?). What acid here liberates the hypochlorous acid? To what class of chemical actions does that on the litmus belong? c. In the hypochlorous acid solution from a place small pieces of (1) litmus paper, (2) paper with printing on it [457], (3) paper with writing in red ink [14] and black ink [612], (4) paper with writing in pencil [433], and (5) colored calico. Observe and record the effect on each (?). Which of these owe their color or blackness to free carbon, and which to colored organic compounds? Does hypochlorous acid oxidize free carbon? Whsit does it oxidize? 75 EXERCISE 37 Chlorates Object: To prepare crystals of potassium chlorate, and to study certain proper- ties of chlorates. Apparatus: Test-tubes. Funnel. Apparatus for generating chlorine* (In- structor). Materials: Potassium hydroxide (sticks). Nitric acid (dil.). Silver nitrate (sol.). Potassium chlorate (free from chloride). a. Dissolve 3 g. (weighed on rough scales) of solid potassium hydroxide in 7 c.c. of water in a test-tube and saturate (Test?) the solution with chlorine. Crystals will appear during the pro- cess of saturation and will increase in quantity as the liquid afterwards cools. Filter off the crystals on a small filter- paper, and examine the filtrate (in b) and the crystals (in c) separately. b. Add to the filtrate dilute nitric acid (this is to destroy potas- sium hydroxide, in case any remains; no equation needed), and then test with a few drops of silver nitrate solution (?). What radical is shown by this test to be present (Exercise 28 a)? What product is thus shown to have V>een formed by the interaction of chlorine and potassium hydroxide? c. Examine the crystals from a with a lens and describe them. Dry the crystals, heat them in a narrow tube, and test for oxygen (?). Dissolve the residue from this operation in distilled water and add silver nitrate solution (?). What substances consti- tuted the crystals and the residue, respectively? From the be- havior of the former sui)stance during making, what do you infer as to its solu})ility? Is the inferonco correct [184]? * Small cylinders of chlorine gas may be used, or the method described in Exercise 26 a and the apparatus of Exercise 16 a may be employed. In either case the experiment should be carried out under a hood, and every precau- tion taken against breathing the gas. 7G CHLORATES 77 d. What effect is observed on adding silver nitrate solution to a solution of yure potassium chlorate? How may the chlorate radical be distinguished from that of the chlorides? The crystals of potassium chlorate made in a are not free from traces of potas- sium chloride (why?), and could not therefore be utilized for this test. What method should you suggest for purifying the chlorate? e. To a minute amount of finely powdered potassium chlorate add two drops of pure, concentrated hydrochloric acid (?). The yellow substance is formed by decomposition of one of the products [270] (?). How would a chloride behave with hydrochloric acid? f. (Optional.) Perchlorates. Dissolve a little pure potassium perchlorate in distilled water and test with silver nitrate solution (?). Explain. To a minute amount of the crystals add two drops of pure concentrated hydrochloric acid (?). How does the result differ from that when potassium chlorate was treated with the same acid? Place about 1 g. of the crystals in a narrow test-tube, heat and test for oxygen (?). How could you distinguish a perchlorate from a chloride, and from a chlorate? EXERCISE 38 Sulphur Object: To study a substance which shows two solid forms and two liquid forms. Apparatus: Test-tubes, Mortar. Watch-glass. Lens (1 for 10 pupils). Trough. Funnel. Materials: Sulphur (roll). Carbon disulphide. Filter-paper. a. Rhombic Sulphur. Place about O.o c.c. of powdered roll sulphur in a dry test-tube, add 2 c.c. of carbon disulphide and shake (?). Pour the solution into a watch-glass and set it aside to evaporate away from all flames. Examine the crystals with the eye and with a lens and make a drawing of two of them (?). Are they brittle or soft? Color? Are they transparent? After 24 hours (or more), are they still transparent? b. Monoclinic Sulphur. Fold a filter-paper as if for filtration, and put water in the trough. Half fill a dry test-tube with roll sulphur. Hold the test-tubie with the clamp from the iron stand and heat very gently, turning the tube in the Bunsen flame, until its contents have completely melted. Dark brown patches show overheating at these points — just-melted sulphur is pale straw- color. Hold the filter-paper by the edge at the three-fold side and pour the melted sulphur into it. \Y^tch the crystals grow. When crystals have formed at the surface and reached the center, pour the remaining liquid sulphur promptly into the trough of water, and open up the paper immediately. Examine the cr^^stals with the eye and with the Ions and make a drawing of two of them (?). Are they brittle or soft? Color? Are they transparent? After 24 hours (or more), are they still transparent? If not, into what form of sulphur have they turned? Examine the part that was poured into water. Is it brittle or soft? Dry a small piece of it and shake it with 1 c.c. of carbon disulphide (?). 78 SULPHUR 79 c. Amorphous Sulphur. Half fill the same test-tube with roll sulphur and melt. Continue heating this time until the sulphur boils and note the changes in color and fluidity which occur (?). Pour the boiling sulphur into the trough of water, moving the tube about during the process. Examine the product. Is it crystalline? Is it brittle or soft? Is it transparent? After 24 hours (or more) is it still trans- parent? After 24 hours (or more), dry a part of it and shake with a little carbon disulphide (?). To find out whether any has dissolved, pour part of the liquid on to a filter, catch a few drops of the filtrate on a watch-glass, and allow them to evaporate (?). What is the insoluble material? Color? Examine with a lens (?). Is it crystalhne? d. Take your three forms of sulphur to the instructor for in- spection and approval. EXERCISE 39 Hydrogen Sulphide Object: To prepare hydrogen sulphide. To study its physical and chemical properties, and to consider uses for them. Apparatus: Test-tube with 1-hole stopper, bent glass tube, and rul)ber tubing. Wide-mouth bottle and glass plate. Materials: Ferrous sulphide (small lumps). Hydrochloric acid (dil.). Lit- mus papers. Cupric sulphate (sol.). Arsenious chloride* (sol.). Mer- curic sulphate (sol.). Lead nitrate (sol.). Antimony trichloride (sol.). a. Take a test-tube fitted with a 1-hole stopper and a bent glass tube (Exercise 3 d), and fit on to the bent glass tube a rubber connection ending in a straight glass tube. Remove the stopper, hold the test-tube almost horizontal, and slip into it carefully about 3 c.c. of ferrous sulphide. Add dilute hydrochloric acid and re- place the stopper. Note the color (?) and odor (?) of the gas. Avoid breathing it, however, as far as possible. b. Place the straight delivery tube in a test-tube half filled with water, so that it reaches the bottom, and let the gas bubble through the water for several minutes. Use the solution in c and d. Now set fire to the gas at the end of the delivery tube (?). What products are formed when the gas burns? c. Smell the solution made in b (?) and test it with litmus paper (?). To what class of substances does hydrogen sulphide belong? What other name is givefT to the solution [328]? Take 4 test-tubes and in each place about 2 c.c. of a solution of a different one of the following salts: (1) Cupric sulphate, (2) Arsenious chloride AsCU, (3) Mercuric sulphate HgS04, (4) Anti- mony trichloride SbCl.i. Add a part of the solution of the gas to each (?). If you do not get good results, pass the gas itself through each solution. What variety of chemical change will an acid and a salt undergo * Dissolve arsenic trio.xide in dilute hydrochloric acid. SO HYDROGEX SULPHIDE 81 in solution [270]? Make equations for the four actions accord- ingly (?). d. A solution of hj^drogen sulphide in water is divided into two parts. To one a few drops of lead nitrate solution are added (?). The other is boiled for five minutes, and a few drops of lead nitrate solution are then added (?). What do you conclude? e. Summarize the observed properties of hydrogen sulphide (?). How could you identif}^ hydrogen sulphide? How could you use it in identifying the metallic radicals in different salts? f. (Optional.) Take about 6 c.c. of sodium hj^droxide solution and saturate it with hj'-drogen sulphide as in b. What is the product [329]? How should you proceed to prepare neutral (or normal) sodium sulphide (solid)? Divide the solution into three parts, and to the first part add dilute hydrocUoric acid (?) Formulate, study and explain this action as in Exercise 28 a, modifying the scheme of formulation to suit the case. To the second part add some bromine-water [303] (?). Allow the third part of the solution to remain exposed to the air for several daj^s (?). When a change in color has occurred, add dilute hydrochloric acid in excess (?). Explain. Have a heart in all experiments that involve the Hberation of hydrogen sulphide or sulphur dioxide, and do not let more of either gas get into the room than you can possibly help. Even if you do not object to the odor, your neighbors probably will. Do not forget, besides, that hydrogen sulphide is actuall}' poisonous if its concentration gets above a certaiQ*hmit [327]. Work under a well-ventilated hood, if available, and don't invite trouble. EXERCISE 40 Hydrolysis Object: To examine several salts in order to find out, by the reaction of the solution, which interact with water ami which do not, and to explain the result in each case. Apparatus : Test-tubes. Materials: Litmus papers. Sodium carbonate (sol.). Cupric sulphate (sol.). Potassium iodide (sol.). Aluminium sulphate. Lead nitrate (sol.). Sodium nitrate. a. Test some sodium carbonate solution with litmus papers (?). Explain the reaction of the solution [330]. b. Repeat a with cupric sulphate solution (?) and explain (?). c. Repeat a \\ith solutions of potassium iodide, aluminium sulphate, lead nitrate, and sodium nitrate (?). Write the equa- tion for hydrolysis in each case (?). Where there is a reaction towards litmus, explain it (?). If there is none, explain why (?). d. Dissolve a single crystal of sodium sulphide in water, and test the solution with litmus paper (?). What ionic substance causes this reaction? Which of the two substances taken is capable of furnishing this ion? Formulate in detail the interac- tion of the two original substances and explain it [329-30]. 82 Il EXERCISE 41 SuiJ»HrR Dioxide Object: To prepare sulphur dioxide arid to study its properties. Apparatus: Watch-glass. Platinum wire. Wide test-tube, 2-hole stopper, funnel, pincb-clamp, rubber and glass tubing. Test-tubes. Wide-mouth bottle, glass plate and cork. Trough- Materials: Sulphur. Sodium bisulphite. Hydrochloric acid (diL). Camar tions or grass or leaves. Apple. a. Place on a watch-glass a {mrticle of sulphur and touch it with a warm platinum wire. (If platinum is not available, a piece of iron wire may be used.) Bring the wire with the adhering sulphur again into the flame. Withdraw and note the color (?) of the flame of burning sulphur and the odor (?) of the gas produced. Name the gas that has this odor (?), and write the equation (?). b. Fit a wide test-tube with a 2-hole stopper, straight tube reaching almost to the bottom, funnel, pinch-clamp, short rubber connection, and short L-tube. iSet this up as in Fig. 22, using the triangle on a ring to support the funnel, and a clamp to hold the test-tube. Test for air-tightness (Exercise 3 d). Place in the test-tube about 10 c.c. of sodium bisulphite, and attach to the L-tube, by means of a rubber connection, a straight glass tube reaching down to the bottom of an upright, dr\- test-tube. Put dilute hydrochloric acid in the fimnel, and admit it drop by drop to the apparatus. If there is little e\idence of action (bubbling), the apparatus may be warmed ver>' slightly to start the reaction. Write the equation. Put water in the trough. Also have ready a bottle containing a moist carnation (or some grass or leaves) and half a sHce of an apple. Leave the other half-shce exposed to the air for com- parison l|iter. Likewise boil half a test-tube full of water for 2 minutes and set aside to cool. S3 Fig. 22. 84 SULPHUR DIOXIDE c. Collect a test-tube full of the gas by upward displacement [117]. Now transfer the delivery tube to the ])ottle, closing the mouth of the test-tube meanwhile with the thumb. Pour quickly a little water into the test-tube and close again firmly. Still keeping the thumb in position, place the mouth of the test-tube under the water in the trough. Notice the level of the water in the test-tube and then remove the thumb (?). Inference (?). d. Cool the boiled water in the test-tube, and again transfer the delivery tube, inserting it to the bottom of the tube containing the boiled water, and let the gas run in for 5 minutes. Cork this tube the instant the delivery tube is taken out, so as to enclose the gas, and not admit air. Keep this solution for use in f and g. Cover the bottle meanwhile or, better still, cork it. After 5 minutes, pass more of the gas into the bottle, and finally cork it again. Observe the color of the contents from time to time (?). Compare the pieces of apple after both have been exposed to the air for a day or more (?). e. Summarize the properties of sulphur dioxide: color (?), odor (?), density compared with air [220] (?), solubility (?), action on vegetable coloring matters (?). f. Use the solution made in d. Test with litmus papers (?). What sort of substance has been formed? Is sulphur dioxide an acidic or a basic oxide [152]? Pour a part of the solution into an evaporating dish, set it on the wire gauze, and boil it [HOOD], noting the odor from time to time (?). Is sulphurous acid stable? g. To the rest of the solution add a couple of crystals of iodine (pulverized in the mortar), shake until the iodine has dissolved, and then add barium chloride solution (?). The precipitate is barium sulphate I^aS04 [344]. Which substance was here oxidized? What substance was If educed? Write equations for the action of iodine (?), and the subsequent action of barium chloride (?). h. Summarize the properties of sulphurous acid: color (?), odor (?), stability (?), oxidizing or reducing agent (?). How should you prepare a solution of sodium sulpj^ite from sulphurous acid? Write the equation. m EXERCISE 42 Sulphuric Acid Object: To learn the properties of concentrated and of diluted sulphuric acid, and to try a test for the sulphate ion. Apparatus : Test-tubes. Glass rod. Evaporating dish. Materials: Sulphuric acid (cone). Litmus papers. Barium chloride (sol.\ Hydrochloric acid (cone). Sodium sulphate. Copper (shav- ings). Copper sulphate (blue-stone") cr>-stals. a. Take 5 c.c. of water and pour into it about 1 c.c. of con- centrated sulphuric acid [Cautiox. Never pour the water into the acid. Why?]. Touch the back of the hand with the bottom of the test-tube (?). b. Apply drops of the solution with a glass rod to red and blue litmus papers (?). c. Boil nearly all the rest of the solution (saving a few c.c. for d below) gently in an evaporating dish with a small flame and note whether there is any odor. After five minutes, test again with Htmus papers (?). Is the acid like sulphurous acid, or is it more stable? Let the dish cool l>efore washing it out. d. Test for the Sulphate Ion SO^^. To the remainder of the solution add bariimi chloride solution (?). Add now 1 c.c. of concentrated hydrochloric or nitric acid (?). Other common salts of barium, if precipitated, would be decomposed and dis- solved by these acids. Write the equation (?). Repeat the test, using a few particles of sodimn sulphate or ammonium sulphate dissolved in water (?). Write the equa- tion (?). e. Twist a few copper sha^'ings into a ball and place them in a test-tube. Add 1 c.c. of concentrated sulphuric acid. Heat gently with a small flame. Note how long it takes to make the acid hot enough to interact at all [Care! Hot sulphuric acid, if spilled, may produce severe burns]. Note the odor (?). Test 85 86 SULPHURIC ACID to see whether any hydrogen is produced (?). Has the sulphuric acid been reduced? Write the equation. What sort of sub- stance is hot concentrated sulphuric acid in this reaction [344]? f. Take in a test-tube about 5 c.c. of concentrated sulphuric acid, place in it a crystal of blue vitriol and let the materials stand for an hour, or more (?). Now heat the contents of the tube to the boihng-point of the acid [HOOD], holding the test-tube in a test-tube holder, keeping it far from the clothing, and taking care that none of the contents spirt out upon the hands or face. After the contents of the tube have settled, decant the clear Uquid into another tube. On the following day, examine the little, shining particles on the sides of this second tube. What is their color, and condition? Of what are they composed [153]? What sort of substance is hot concentrated sulphuric acid in this reaction [344]? g. Summarize the properties of the acid: State (?), color (?), odor (?), stability (?), action on litmus (?), action on water (?), on barium chloride (?), on elements like copper (?), on hydrates like blue vitriol (?). Be very cautious in all of your dealings with hot concentrated sulphuric acid. It is good neither for the clothes nor for the skin. On no account empty the residual acid in c, e, or f into the sink until it is quite cold, or you may need a new pair of eyes. It is not worth while taking any chances. EXERCISE 43 Nitrogen from the Air Object : To obtain nitrogen from the air by removing the oxygen, and to study its properties. Apparatus : Large bottle with 2-hole stopper, glass and rubber tubing. Hard glass tube, 12 inches long, with two 1-hole stoppers. Trough. Wide- mouth bottles. Materials : Copper gauze. a. Set up the apparatus as shown in Fig. 23, and connect the rubber tube on the left with the water supply. Roll up the copper gauze and insert it in the middle of the hard glass tube. /Vafer Copper Gauze ^Nitrogen 1 -^-_-\v-_- Fig. 23. b. Heat the copper gently at first, using a Bunsen burner with a wing-top (?). Increase the flame gradually until the whole length of the gauze is strongly heated. Now turn on the water carefully so that the air in the large bottle is slowly displaced and driven over the hot metal. c. Collect two bottles of the gas that passes over into the trough, and cover the mouth of each with a glass plate. Test 87 88 NITROGEN FROM THE AIR the first with a hghted taper (?). Leave the second uncovered for a few minutes and test with a taper again (?). d. Examine the gauze after it has cooled. How has its appear- ance been changed? What is the material formed? Write the equation (?). How could you prove this and, at the same time, recover the gauze in its original form [135]? e. (Optional.) Nitrogen from Its Compounds. Place about 10 g. of pure sodium nitrite and about 8 g. of ammonium chloride in a 250 c.c. flask fitted with safetv and deliver}^ tubes (Fig. 16, p. 33). Clamp the flask by the neck to a ring-stand, add about 15 c.c. of water, and warm gently [Cautigx], As soon as the action begins, remove the flame, bring a dish of cold water under the flask, and cool it for a few seconds at a time so that the action may not become too violent, but may run uniforml}-. After sufl?icient time has been allowed for the displacement of air from the apparatus, fill a bottle with the gas over water in a pneumatic trough. Has the gas odor or color? Does it support combustion? Write the equation for the reaction in detail. How does the product in this experiment difi'er from that obtained in c? I) pi EXERCISE 44 Carbon Dioxide in Air and in the Breath Object: To show the presence of carbon dioxide in atmospheric air and in ex- pired air. Apparatus: Beaker. Glass tube. Test-tube. 2 wide-mouth bottles, and glass plates. Trough. Materials: Barium hydroxide (sol.). Taper. Limewater. a. Place about 3 c.c. of clear barium hydroxide solution in the bottom of a clean beaker and leave it exposed to the air for half an hour or more (?). Barium hydroxide Ba(0H)2 behaves towards carbon dioxide like limewater, but, being more soluble than calcium hydroxide, its solution is more concentrated and a more copious precipitate can be obtained. Explain the result (?), and write the equation for the action (?). b. Blow air from the lungs through a straight tube into 5 c.c. of limewater (?). c. Fill two bottles with water and invert them in the trough. By means of a tube, fill one with air from the lungs immediately after drawing a breath. Fill the other with air after the lungs have been almost emptied. Slip a glass plate under each bottle and set both upright on the table. Light a taper and plunge it into one bottle (?) and then into the other (?). Explain the result (?). 89 EXERCISE 45 Ammonia Object: To gttidy two waya of obtaining ammonin ovA to ohnerve its physical and chemical j/ropeHies. Apparatus: Te8t-tu>x«. 1-hole stopper, L-tube, and perforated cardboard. 1 wide-mouth bottles, and glass plates. Glass roe full of ammonium chloride and mix it thorougbly on pafKT with an erjual volume of slaked lime. Plaee it in a test-tul)e provided witli a one-hole stopf)er and I/-tube long enough to reach the bottom of the inverted bottle (Fig. 24). Clamp the i\i\yo so that the moutli P m- Via. 24. I« AMMONIA 91 is inclined very slightly downwards (to prevent condensed moisture running back). Arrange the perforated card on a ring, and first slip an inverted test-tube over the L-tube. Provide a test-tube containing a few drops of concentrated hydrochloric acid. Also, place water in the trough. Warm the mixture very gently with a small flame. Dip the end of a thin glass rod in the hydrochloric acid, and bring it close to the perforation in the card to ascertain when the test- tube is filled with the gas. Dense smoke will notify you of this condition. Remove the test-tube, closing it firmly with the thumb, and with the other hand set a bottle (to be used in e) over the L-tube. d. Place the mouth of the test-tube under water and remove the thumb (?). Is the gas soluble in water? How does its be- havior compare with that of chlorine (Exercise 25 a) in this respect? e. Warm a second bottle by moving it rapidly through the flame. Do not let it rest in the flame or it will crack. Place in the bottle a few drops of concentrated hydrochloric acid, cover it with a glass plate, and rotate it horizontally so as to spread the acid as completely over the inner surface as possible. Now, ascertain by use of the rod dipped in hydrochloric acid (refer to c above) whether the first bottle is full of ammonia. When it is, raise it off the tube, and slip a glass plate under the mouth. Bring the two bottles mouth to mouth and remove both plates. Invert the pair of bottles once or twice to mix the gases (?). What is the deposit? Describe its physical properties (?). Write the equation for the action (?). f. Swing the L-tube downwards so that its free end is just above (but not touching!) the surface of about 5 c.c. of water in the bottom of a beaker. At the end of 5 minutes pour the solution into a test-tube, cork it up, and reserve for use in Exercise 46. During the five minutes, swing the water round in the beaker occasion- ally to submerge the surface layer. Concentrated ammonia has a density of 0.88, i.e., 1 c.c. weighs 0.88 g. Will the solution float or sink? What difference would it make if the beaker were left at rest? Contrast with Exercise 21 b. g. Summarize the observed properties of ammonia (?). EXERCISE 46 Hydroxide and Salts of Ammonium Object: To observe the properties of anwionium hydroxide and of salts of am- monium, and to learn a test for the latter. Apparatus: Glass rod. Evaporating dish. Beaker. Test-tubes. Materials: Litmus papers. Hydrochloric acid (dil.). Ammonium chloride. vSodium hydroxide (sol.). Ammonium sulphate. a. Ammonium Hydroxide. Dip a rod in the solution made in Exercise 45 f and touch litmus papers with it (?). To what class of substances does the material in solution belong? Write the equation for the formation and reaction of this material (?). b. Pour a part of the solution into an evaporating dish and boil it. From time to time observe its odor and reaction towards litmus papers (?), proceeding meanwhile with c. What must have happened to the compound in the solution? Is it a stable or an unstable compound [406]? Write the complete equa- tion (?). c. Place the rest of the solution in a beaker, add dilute hydro- chloric acid a little at a time, stirring with a rod and testing the liquid on litmus papers until the liquid is neutral. Evaporate the liquid in a dish almost (but not quite) to dryness (lower the flame towards the end), allow it to cool and describe the residue (?). Write the equation (?). d. Ammonium Salts. Place not over 0.2 c.c. of ammonium chloride in the bottom of a dry hard glass test-tube. Clamp the latter in a horizontal position, and place in the mouth of the tube moistened litmus papers (red and blue). Heat the salt and watch the test papers for any changes and describe them (?). Is there evidence that the salt decomposed? What were pre- sumably the products? Make the equation (?). Would these products recombine (partially at least) in the cool part of the tube? Is there any sublimate visible (?) and if so, what is it? 02 HYDROXIDE AND SALTS OF AMMONIUM 93 e. Test for Salts of Ammonium. Take 2 c.c. of sodium hydrox- ide solution and add a few particles of any salt of ammonium (for example, the sulphate). Warm, and observe the odor (?). Write the equation as a double decomposition (?). Which of the products decomposes further to give the ammonia? EXERCISE 47 Nitric Acid Object : To prepare nitric acid, to study its properties, and to try to test for a 7iitrate. Apparatus: Tubulated retort (glass stopper). Flask. Trough. Funnel. Materials: Sodium nitrate. Sulphuric acid (cone). Woolen yarn (white). Copper (shavings). Splints. Zinc (gran.). Ferrous sulphate (sol.). a. Put about 20 g. of sodium nitrate in a tubulated retort. Insert the neck of the retort into the mouth of a flask (Fig. 25). Clamp the retort so that the body rests on the wire gauze over a tripod and the flask is partly im- mersed in a vessel of cold water. Through a funnel or thistle-tube pour about 15 c.c. of concentrated sulphuric acid upon the sodium nitrate, place the stopper in the retort, and wait until the acid has moistened the entire mass. Caution: Sulphuric acid and nitric acid both produce severe wounds on the flesh and destroy clothing. Do not get careless with nitric acid in your laboratory work, or you will find, just as Professor Remsen of Johns Hopkins University did before you,* that it acts upon copper, fingers and trousers with equal vigor. The nitric acid to be prepared is 100' f, and the greatest care must be used in handling it. With large classes, sections a and b of this experiment are preferably performed in the lecture-room. Heat the retort very gently [HOOD], and distil at as low a tem- perature as possible until no more nitric acid condenses in the • See Harrow, Eminent Chemiata oj Our Time, D. Van Nostrand Co., 1920, p. 200. 94 Fig. 25. ( NITRIC ACID 95 neck of the retort (meantime, proceed with c). Allow the retort to cool before touching it. What is the brown gas seen in the retort (?), and whence does it come [411]? What is the residue in the retort? Write the equation. Do not try to improve upon the set-up in the above preparation by intro- ducing a cork between the retort and the flask. It is a common mistake for students to think that they ought to do this to prevent any nitric acid fumes from escaping; they forget that the cork hermetically seals up the apparatus. Fortunately few of them can make the connection really air-tight, or they would be hurt more often. b. Divide the distillate between four dry test-tubes. In one place a piece of white woolen yarn (?), in the second a small piece of copper (?), in the third a piece of a splint (?), and in the fourth a small piece of zinc (?). The action on copper is a test for nitric acid, by itself, or mixed with other substances. Write the equation. What gas does zinc displace from other acids? What gas is produced, with zinc, here? Write the equation. c. Test for the Nitrate ion NOs" (follow the directions with care). Pour into a test-tube 3 c.c. of ferrous sulphate solution. Add to it two drops of dilute nitric acid and shake. Incline the tube very slightly, and pour concentrated sulphuric acid (not over 2 c.c.) in a steady stream down the wall of the test-tube so that (being a heavy liquid) it flows to the bottom and collects below the ferrous sulphate solution (?). Describe the coloration in the layer where the liquids meet (?). Repeat the test, adding a small crystal of sodium nitrate, in- stead of the nitric acid, and shaking. How should you recognize an unknown substance to be a nitrate? Devise a second test with the help of section b above. d. Summarize the properties of nitric acid (?). EXERCISE 48 Nitric Oxide Object: To observe the action of dilute nitric acid on copper. To prepare nitric oxide and study its properties. To observe part of the process used in the fixation of atmospheric nitrogen. Apparatus: Gas generating bottle (90 c.c), 2-hole stopper, thistle, L and delivery tubes. Trough. Wide-mouth bottle. Graduated cylinder. Test-tubes. Deflagrating spoon. Glass plate. Wide test-tube, 2-hole stopper, dropper, L and delivery tubes. Materials: Copper (shavings or clippings). Nitric acid (cone). Taper. Phosphorus (red). Sodium peroxide. Litmus papers. a. Fit up a generating bottle as in Fig. IG (Exercise 15 a). Place in it copper shavings or clippings. Invert one bottle, one test- tube, and the graduated cylinder, all full of water, in the trough. Pour some water through the thistle- tube, and an equal volume of concentrated nitric acid, and wait for the action to start. Then fill the bottle and test-tube with the gas, collect about 30-40 c.c. (only) of the gas in the graduated cylinder, and leave them stand- ing in the trough. Note the color of the gas in the generator just after the beginning of the action (?) and again later (?). Note also the colo^ of the liquid in the generator. This is characteristic of cupric salts, and is the color of the cupric-ion Cu+^". b. What is the color of the gas? Use the test-tube full of the gas to test its solubility in water as in Exercise 41 c (?). What happens when the test-tube is opened to the air (this action is examined further in d)? c. Place in the deflagrating s[X)on a little red phosphorus. Cover the bottle full of the gas with a glass plate, and set it upright on the table. Plunge a burning taper into the gas (?), withdraw it instantly, and cover the bottle. Set fire to the phosphorus, 96 Fig. 26. NITRIC OXIDE 97 and when it is burning vigorously, plunge it into the same bottle (?). Write the equation. Heat the spoon, to burn off the adhering phosphorus, before putting it away. d. Fit a wide test-tube with a 2-hole stopper, L-tube and rubber delivery tube, and a dropper (Fig. 26). Place in the test-tube about 1 c.c, of sodium peroxide. Fill the dropper with water, and immerse the delivery tube in the trough. Pinch the dropper cautiously so as to allow one drop of water at a time to fall on the peroxide. When the air has been displaced from the test-tube and dehvery tube (test?), read the volume of the gas collected in a in the graduated cylinder (?), and allow the oxygen to ascend, a few bubbles at a time, into the latter (?). Note the change in color (?). Slightly shake the water in the cylinder to bring it in contact with the gas. Does the volume change (?) and, if so, in which direction? Remember that oxygen gas is being added. Finally, close the cylinder with a glass plate, set it upright, and test the water in it with blue litmus paper (?). Write the equations for all the reactions that occur in this section. e. Which component of the air caused the nitric oxide to be- come brown in b? What is the brown gas? What property of the brown gas have you learned in d? What reaction to litmus had the water in the cylinder (?) and what was the substance formed [413]? What great industrial process is based on this reaction [414]? f. Summarize the properties of nitric oxide (?). EXERCISE 49 Nitrous Oxide Object: To prepare nitrous oxide and to study its properties. Apparatus: Test-tube, 1-hole stopper, L and delivery tubes. Test-tubes. Wide-mouth bottle. Trough. Deflagrating spoon. Materials: Ammonium nitrate. Splints. Asbestos paper. Sulphur. a. Preparation of Nitrous Oxide. In a large test-tube pro- vided with a 1-hole stopper and rubber and glass delivery tube, place 10 g. of ammonium nitrate. Clamp the test-tube at an angle of 45°. Fill one bottle and two test-tubes with water and invert them in the trough (use warm water, if available). Heat the nitrate cautiously but continuously with a small flame, and allow^ the gas to come very slowly. If, before the vessels are filled with gas, the nitrate threatens to give out [explosion possible], first remove the delivery tube from the trough, then stop heating, and add more ammonium nitrate. Watch the water in the delivery tube. Does anything else appear to Ix? produced along with the nitrous oxide gas? What is it? Be careful, in this experiment, not to let the reaction run away from you. The decomposition of ammonium nitrate evolves heat, and you do not want to induce such a rapid rush of gas that your apparatus will blow up. There is absolutely no danger in this experiment if you follow instructions, but the picture opposite p. 415 of the GeneratVhemistry will demonstrate to you what can happen when a large amount of ammonium nitrate suddenly decomposes. b. Use one test-tube of the gas, as in Exercise 41 c, to find out whether the gas is soluble in cold water (?). Docs the gas differ from oxygen in this respect? c. Into the second test-tube thrust a glowing splinter (?). Does the gas differ from oxygon in this respect? d. Line the deflagrating spoon with asbestos paper and place on it a little sulphur. Set fire to the sulphur, without heating I NITROUS OXIDE 99 the spoon. Immediately, while it is still burning feebly, thrust it into the bottle of the gas (?), and then remove it and cover the bottle. Heat the spoon until the sulphur burns briskly and thrust it into the bottle once more (?). How does the gas differ in behavior from ox^^gen? Note the odor in the bottle (?). What is formed when sulphur is burned in nitrous oxide? e. Summarize the properties of nitrous oxide: color (?), solu- bility (?), density compared with air (?), supports combustion, how well (?). f. Name two respects in which nitrous oxide differs from oxygen (?). When nitrous oxide is added to nitric oxide, no brown gas (Exercise 48 d) is formed: this is another difference. Devise a means of testing this statement experimentall3^ Submit your arrangement to the instructor for approval before trying it. g. (Optional.) Take 2-3 g. of sodium nitrate in a hard glass test-tube, and heat strongly and persistently with the blast lamp until the evolution of gas ceases. Test the escaping gas for oxygen. What nitrates behave in this way when heated? When the residue has cooled, add not more than 3 c.c. of w^ater, shake vigorously until the whole has dissolved, and add dilute sulphuric acid (?). How could a nitrite be distinguished from a nitrate? How does lead nitrate behave when heated? Write the equa- tion and devise a method for demonstrating each product experi- mentally. What other nitrates behave in the same way? How does ammonium nitrate behave when heated? EXERCISE 50 Phosphine and Phosphoric Acid Object: To prepare phosphine and to observe the reactions of phosphoric add or phosphates. Apparatus: Test-tubes. Glass-tubing. Mortar. Dropper. Materials: Calcium phosphide. Litmus papers. Phosphoric acid (sol.) or sodium phosphate. Ammonium molybdate (sol.*). Silver nitrate (sol.). Ammonium hydroxide (sol.). Nitric acid (cone). a. Phosphine. Drop a small piece of calcium phosphide, Ca3P2, half the size of a pea, into 3 c.c. of water in a test-tube (?). The gas evolved is phosphine PH3. Note the odorf (?). Is the gas combustible? Is its kindling temperature low or high? Test the reaction of the water with litmus papers (?). What must the dissolved substance be? Write the equation for the action of the calcium phosphide on water, also that for the burning of phosphine in air (P2O5 is formed). b. Test for the Phosphate Radical. To 10 c.c. of water add not over 1 c.c. of phosphoric acid H3PO4 (or 0.5 c.c. of sodium phosphate). Take 5 c.c. of ammonium molybdate solution, add to it 2 drops (not more, reserve the rest for c) of the phosphoric acid solution and warm the mixture (?). This is a test for the radical of orthophosphoric acid (PO4) and the orthophosphates. c. To the rest of the phosphoric acid solution add silver nitrate solution, shaking and adding more until a permanent precipitate is formed (?). The precipitate is silver orthophosphate Ag3P04. Write the equation (?). * 70 g. ammonium molybdate and 180 c.c. nitric acid to make 1 liter of solution. t Do not get too friendly with {)hosphine. Its smell is intensely disagree- al)le, and the gas is actually poisonous. Waft the gas gently towards you with your hand; do not put your nose tlirectly over the mouth of the tube. 100 i » f 1 I 'U EXERCISE 51 Arsenic Trioxide Object: To observe the reduction of an oxide hy carbon and to study the proper- ties of arsenic trioxide. Apparatus : Glass tubing. Test-tubes. Materials: Arsenic trioxide. Charcoal (powdered). Hydrochloric acid (cone). Sodium hydroxide (sol.). a. Draw out a piece of glass tubing to make two ignition tubes each 7 cm. long. Place in the closed end of one a very small amount of arsenic trioxide. Heat the oxide, and watch the cold part of the tube for a sublimate [297] (?). Is the oxide volatile? Does it melt before vaporizing? b. Place a small amount of arsenic trioxide in the other tube, and above it a little powdered charcoal. Heat the oxide and the charcoal, and examine the cold part of the tube [426] (?). What change has the oxide undergone? c. Take about 0.5 c.c. of arsenic trioxide in a test-tube, add 2 c.c. of water and warm (?). Now add 1 c.c. of concentrated hy- drochloric acid and heat again (do not boil!) (?). To what class of oxides does arsenic trioxide appear to belong? Write the equa- tion (?). Set aside and examine later. Is the action reversible [541]? d. Take about 0.5 c.c. of arsenic trioxide, add 2-3 c.c. of sodium hydroxide, and warm (?). To what class of oxides does it appear now to belong? 101 EXERCISE .52 Carbon Object : To observe the jrroduction of carbon dioxide when wood bums and when oxifles of metals are red^xced by carbon. Apparatus: 2.vO c.c. bottle. Mortar. Trip scales. Hard glass test-tube with 1-hole stopper and L-tube. Materials: Limewater. Splints. Cupric oxide ^powdered;. Charcoal ^powdered). a. Place 10 c.c. of limewater in a 250 c.c. bottle. Burn a splinter of wood in the Vjottle, taking care not to drop any ashes into the liquid. Close the bottle with the hand and shake (?). If the change is not distinct, repeat the burning, using the same limewater, and shake again. What elements does wood contain? Make the equations for the formation of the carbon dioxide and for its reaction with the limewater. b. Mix intimately in the mortar 5 g. of cupric oxide and 0.5 g. of powdered charcoal. Place this on a strip of paper, folded \- shaped, slip it into the hard-glass test-tube held horizontally, tilt so as to slide the mixture to the bottom of the tube, and withdraw the paper. Insert the stopper and L-tube. Place 10 c.c. of limewater in a test-tube. Clamp the tube containing the mixture in a horizontal position, at such a height that it can be heated, and let the L-tulxi project to the bottom of the limewater. If the tube is too short to reach the bottom, add a straight glass tulx; and rubber connection. The purpose is to compel any gas which may be given off to bubble through the entire depth of the lime- water. Heat the mixture, beginning at the end farthest from the stopper, at first gently and then strongly and persistently until buVjbles almost cease to pass. What changes take place in the limewater [439, 561]? Finall}', take the tube out of the limewater and then remove the flame. When the tulje is cold, grind the UY2 1^ CARBON 103 contents in the mortar with water, and wash away the Hghter particles. Examine the residue (?). Make the equation for the action (?). What important industrial processes depend on this reaction? What was oxidized and what reduced in this reaction? EXERCISE 53 Carbon Dioxide Object: To prepare carbon dioxide and to observe its properties. Apparatus: Gas generating bottle (90 c.c), 2-hole stopper, thistle tube, L-tube and rubber delivery tube. 3 wide-mouth bottles (250 c.c.) and glass plates. Test-tubes. Taper. Materials: Marble (chips). Hydrochloric acid (dil,). Litmus (sol.). Lime- water. a. Use the apparatus in Fig. 16, Exercise 15 a. Slide into the bottle (do not drop them in) enough marble chips to fill it to a depth of one inch, and connect. Add dilute hydrochloric acid and fill all bottles with the gas by upward displacement of air. Cover the bottles with glass plates. To a test-tube (clean) full of water add some litmus solution. Pour half of the mixture into another test-tube and keep the latter for reference. Through a clean glass tube, pass carbon dioxide into the other half (see c). b. Light a taper and pour the gas from one of the bottles over the flame, as you would water (?). Does the gas support com- bustion? Is the gas heavier or lighter than air? Give the reason for your answer (?). To learn whether the gas is soluble in water, pour about 10 c.c. of water into a bottle of the gas, cover quickly and firmly with the palm of the hand, and shake vigorously. Is the hand hold against the mouth of the bottle by atmospheric pressure, or not? Is the gas soluble? c. Examine the litmus solutions, and compare their color (?). What property has the solution of carbon dioxide in water? How is the substance formed (equation)? d. Make a list of the properties observed: Color (?), odor (?), density (?), solubility (?), supports combustion or not (?), what 104 I CARBON DIOXIDE 105 chemical action on water (?). Note which of these properties are physical and which chemical (?). e. If you obtained a carbonate as an unknown substance, how should you proceed to identify it? f. (Optional.) Lead the gas into a little sodium hydroxide solution in a test-tube until the solution is saturated. Let the solution stand until it dries spontaneously^ (first residue). Heat the dry residue (?) in a test-tube, and determine what two things are given off. To this residue after heating (second residue) add dilute hydro- chloric acid until all action (?) ceases. Evaporate the solution on the water bath, and examine and taste this final residue (?). Having recognized the products of the last action, and taking into account the preceding observations, state what the nature of the second and first residues must have been (?). Write equations for all actions (?). EXERCISE 54 Carbon Monoxide Object: To prepare carbon monoxide and to observe its properties. Apparatus: Flask (200 c.c.) with 2-hole stopper. Funnel, pinch-clamp, straight tube and rubber connection. L-tul)e and delivery tube. Trough. 3 wide-mouth bottles (250 c.c). Glass plate. Round-bottomed flask (250 c.c). Materials: Sulphuric acid (cone). Formic acid. Limewater. Taper. Caution: The gas is poisonous (HOOD\ Do not allow it unnecessarily to escape into the room. With large classes it is safer to perform this experiment as a lecture demonstration. a. Fit a 200 c.c. flask with a 2-hole stopper, L-tube and rubber delivery tube, and the funnel and straight tube with pinchclanip as shown in Fig. 22 (Exercise 41). Place the flask on the ring of the iron stand (with wire gauze), at a suitable height for heat- ing by a small flame. Hold the funnel erect in the clamp. Ex- tend the deliver^' tube, if necessary, by adding a bent glass tube so that the gas may be collected over water. Remove the stopper, pour into the flask about 1 cm. depth of concentrated sulphuric acid, and replace the stopper. Pour some formic acid (care!) into the funnel, and never allow this entirely to run out during the experiment. Be careful to wash off any acid that you got on your hands immediately (?). Warm the sulphuric acid gently (small flame), and then admit the formic acid a drop or two at a time. Collect three bottles full of the gas. What will the first bottle largely contain? Do not, under any eireu^nstanees, bring it near an open flame. What would happen if you were foolish enough to attempt to introduce a lighted taper into it? Let the bottle stand on the desk, open and mouth upwards, for a full minute. Now (not before!) try the lighted taper experiment (?). Explain. b. Light a taper, raise the second bottle out of the water and 106 \ fi CARBON MONOXIDE 107 plunge the taper up into it. Does the gas burn? Does the taper burn in the gas? c. Slide the glass plate under the third bottle of the gas and remove from the trough. For a moment, move the plate to one side sufficiently to pour in a little limewater, taking care to let as little gas escape from the bottle as possible. Shake (?). Now light a taper, set fire to the gas in this bottle, replace the cover instantly, and shake again (?). What product is formed when carbon monoxide burns? Make the equation (?). d. Molecular Weight of Carbon Monoxide [Quant.]. Obtain [Storeroom] a round-bottomed, 250 c.c. flask. Fit it with a rubber stopper through which passes a short, straight tube. Attach to the latter a short piece of rubber tubing closed with a strong pinch- clamp. Make a mark on the neck at the bottom of the stopper, so as to be able to measure the exact content of the flask up to the stopper. Place 30 c.c. of water in the flask, insert the stopper, remove the clamp, and boil the water with a small flame for about five minutes, so as to drive out all the air. Close the rubber tube with the clamp and remove the flame quickly, wipe the flask and allow it to cool. When it has assumed the temperature of the air, weigh the whole carefully, suspending the flask on the balance by a thread tied round the neck (?). Connect with the apparatus delivering pure carbon monoxide, and open the clamp a very little so as to admit a slow stream of the gas. When the flask is full, close the clamp, disconnect from the generating apparatus, open the clamp for an instant to restore the pressure to that of the at- mosphere, and weigh again (?). The gain in weight represents the weight of the carbon monoxide. Read the barometer and thermometer (?). Subtract from the barometric reading the aqueous tension at the observed temperature. Ascertain the volume of the flask by filling with water to the mark from the graduated cylinder. Calculate the weight of the G.M.V. of the gas (?). To what class of gases would this method of determining the density and molecular weight be applicable? Why could not this method be used for carbon dioxide? e. Summarize the properties of carbon monoxide: color (?), 108 CARBON MONOXIDE solubility in water (?), burns or not (?), supports combustion or not (?), density compared with air (?). How could you distinguish burning hydrogen from burning carbon monoxide? *■ I EXERCISE 55 Methane and Acetylene Object: To make two typical hydrocarbons, to ascertain their properties, and to compare the luminosities of their flames. Apparatus: Test-tube. 1-hole stopper and L-tube. 250 c.c. bottle. 12- inch rubber tube. Evaporating dish. Beaker. Materials: Soda-lime. Sodium acetate (powdered, anhydrous). Lime- water. Litmus papers. Hydrochloric acid (cone). Calcium carbide. a. Methane. Mix about 2 c.c. each of powdered soda-lime and sodium acetate and place the mixture in a test-tube. Clamp this in a horizontal position* and insert in it a 1-hole stopper with L-tube pointed upwards. Tap the test-tube to cause the mixture to settle and heat it gently (small flame). Slip a test-tube over the vertical part of the L-tube. When the gas in this test-tube, on being lighted (after removal to a distance), burns quietly, set fire to the jet issuing from the apparatus. b. Describe the structure of the flame (?). How luminous is the flame? Hold a bottle so that the flame burns inside it. If a dew appears in the bottle, what is it? Inference (?). Withdraw and close the bottle, and shake the contents with some lime water (?). Inference (?). Extinguish the flame, and test the gas for acid or basic properties by holding in it moistened strips of red and blue litmus paper (?). Summarize the observed physical and chemical properties of the gas (?). c. Acetylene. Fill a test-tube with water. Invert it in an evaporating dish partly filled with water. Place a small piece of calcium carbide in the water, and collect the gas in the test-tube. Set fire to the gas in the test-tube. Compare the luminosity of the flame with that of methane (?). Close the tube, add a * If you do not clamp j^our tube in the position indicated, you will certainly crack it during the experiment. 109 110 METHANE AND ACETYLENE little limewater and shake (?). Inference (?). Summarize the observed physical and chemical properties of the gas (?). d. Pour the liquid in the evaporating dish into a beaker (?). Test it with litmus papers (?). What is the suspended sohd? Write the equation for the interaction of the carbide and water (?). e. (Optional.) Ethylene [HOOD]. Fit a 250 c.c. flask with a doubly-bored cork, through which pass a dropping-funnel and L-tube. Attach a gas-washing bottle containing a little water, and connect an L-shaped delivery tube. Test the apparatus to see that it is air-tight. Place in the flask about 20 g. of phosphorus pentoxide, and clamp it to a ring-stand over a sand bath. Intro- duce into the bulb of the dropping-funnel some alcohol. Finall}^ heat the phosphoric anhydride, and admit the alcohol drop by drop. Fill a bottle with the gas (not sl mixture of the gas and air (?) ) over water and apply a light (?). Quickly pour some limewater into the bottle, and shake (?). Attach a nozzle to the exit tube of the washing-bottle and raise the other tube clear of the water in the washing-bottle (why?), ignite the gas, and observe the luminosity of the flame. What commercial use has ethylene [458]? Hold a cold, dry beaker over the flame (?). What are the products of complete combustion of all hydrocarbons? I Ipl il EXERCISE 56 Starch and Sugars Object: To study the properties of starch and its hydrolysis into glucose; and to learn the properties of two sugars, glucose and sucrose (ordinary sugar) . Apparatus: Test-tubes. Flask. Funnel. Beaker. Glass rod. Graduated cylinder. Materials: Fehling's solution No. 1 and No. 2* Starch. Hydrochloric acid (cone). Potassium iodide (sol.). Iodine. Sodium carbonate (sol.). Litmus papers. Sugar. Molasses. a. Starch and Glucose. Shake about 0.5 c.c. of starch with 20 c.c. of water and then boil (?). Add a few drops of the hquid to 5 c.c. of Fehling's solution and warm the latter (?). Does starch change Fehling's solution? Place three-fourths of the remaining starch suspension in a flask, set it on the wire gauze, add 5 or 6 drops of concentrated hydrochloric acid, and boil gently for ten minutes. Place the funnel in the mouth of the flask, to diminish the loss by evapora- tion, and add a little water when necessary so as to keep the volume constant. b. While this is going on, cool the rest of the starch suspension in running water and. pour it into a beaker nearly full of cold water. Add one drop from 5 c.c. of a solution of potassium iodide in which a single crystal of iodine has been dissolved (?). c. Cool the contents of the flask (from a) and add sodium carbonate solution drop by drop, shaking between drops, and touching the edge of a piece of litmus paper with a glass rod dipped in the liquid, until the liquid gives faint alkaline reaction. Now add a few drops of this liquid to 5 c.c. (measured) of Fehling's solution and warm the latter [466] (?). Add more of * No. 1: 69.3 g. of CuS04,5H20 with water to make 1 liter. No. 2: 350 g. Rochelle salt and 100 g. sodium hydroxide with water to make 1 liter. Mix equal volumes (measured) just before use. Ill 112 STARCH AND SUGARS the liquid, boil again, and continue until the blue color is gone. It takes 0.005 g. of glucose to reduce and decolorize 1 c.c. of Fehling's solution. What amount of glucose was contained in the part of the liquid you added? d. Sucrose. Dissolve about 0.5 g. of sucrose (ordinary sugar) in 20 c.c. of water and repeat a and c with this liquid. Does sucrose reduce Fehling's solution? Do acids hydrolyze it to give glucose? Write the equation. The hydrogen-ion of the acid acts as a catalyst. Why is it not included in the equation? e. Dissolve about 0.5 c.c. of molasses in water and test for glucose as in a, par. 1 (?). f. Tabulate the physical and chemical properties of starch, glucose, and sucrose separately as follows: color (?), solubility (?), action on Fehling's solution (?), action of dilute acids (?). I EXERCISE 57 Acid and Alkaline Soils Object: To ascertain whether a soil is acid or alkaline, and to measure the acidity of an acid soil. Apparatus: Watch-glass. Wide-mouth bottle. Graduated cylinder. Bu- rette. Beaker. Glass rod. A^aterials: Soil. Potassium nitrate (sol.). Sodium hydroxide (sol.). Phe- nolphthalein (sol.). a. Litmus Test. Place a red and a blue piece of litmus paper on a large watch-glass. Make the soil to be tested into a paste with distilled water, and press it on to the litmus papers. Place another watch-glass on top of the first, so as to hold the soil against the paper for 15 minutes. Note whether the soil gives an acid or an alkaline test. b. Measurement of Acidity in Soil. Place 100 g. of an acid soil in a 400 c.c. (or 12 oz.) wide-mouthed bottle. Add 250 c.c. of normal potassium nitrate, stopper the bottle, and shake the bottle by hand at intervals of five minutes. Let the mixture stand overnight. Withdraw 125 c.c. of the clear liquid from the top, boil it for ten minutes to expel carbon dioxide, cool it, and titrate with normal solution hydroxide, using phenolphthalein as indica- tor. Tabulate the results: (1) Titration c.c. NaOH (2) Titration c.c. NaOH Average c.c. NaOH Calculate how much calcium carbonate would be required to neutralize the soil. 113 EXERCISE 58 Fertilizers Object: To teat the efect of certain fertilizer n en crops. Apparatus: Large jars. Materials: Ammonium nitrate. Monocalcium or di-fiodium phosphate. Potaaaiitm sulphate. Soil. Seeds. a. Essential Plant-foods. Nitrogen: Dissolve 16 g. of am- monium nitrate in 500 c.c. of distilled water. Phosphorus: Dis- solve 5 g. of mono-calcium phosphate, or di-sodium phosphate, in 500 c.c. of distilled water. Potassium: Dissolve 10 g. of potas- sium sulphate in 500 c.c. of distilled water. Prepare these solu- tions carefully, using chemically pure salts, and label each bottle. b. Pot-culture Test for Plant-food Requirements. Procure sufficient of a poor quality of soil to fill eight ordinary- four-gallon butter jars. In the center of each pot make a drainage hole about § inch in diameter, cover this ^nth a copper-wire netting, and place upon this a piece of glass wool extending over the hole. Fill each pot with the soil, pressing it in firmly. Plant the series with wheat, oats, or other suitable crop. Re- move the surface layer, distribute the seed, and return the soil removed. Use sufficient seeds so that a uniform number of strong seedlings may be left in the pot (about 20 seeds). Place the pots either in a greenhouse, or in th^ open, but so that they will be protected from .severe wind or hea\'y rain. Water regularly. To the first pot add no fertilizer. To the remaining pots add, at the time of planting, and weekly thereafter, 10 c.c. of the pre- pared solutions, as follows: Pot 2, Ammonium nitrate; Pot .3, Phosphate solution; Pot 4, Potassium sulphate; Pot 5, Ammonium nitrate and phosphate solution; Pot 6, Ammonium nitrate anrl potassium sulphate; Pot 7, Phosphate solution and potassium sulphate; Pot 8, All three solutions. 114 ( FERTILIZERS 115 c. When mature, the crop should be harvested uniformly, and weighed. Afterwards, separate the grain from the straw, and weigh the grain. Compare the yields secured from the different fertihzers. What conclusions do you draw from your results? EXERCISE 59 Fermentation Object : To ferment some molasses and to study some of the properties of alcohol* Apparatus: Large bottle (2 1.) or flask, 1-hole stopper to fit, with L-tube, delivery tube and glass tube. Distillation apparatus (Fig, 17, Exercise 17). Wide-mouth bottle. INIortar. Materials: Molasses. Yeast. Limewater. Litmus papers. Asbestos wool. a. Mix 250 c.c. of molasses with 1500 c.c. of water in a bottle or large flask. Break up a cake of yeast, shake it with water until it is completely suspended, and add it to the molasses. Plug the mouth of the bottle loosely with cotton, and set the whole in a warm place for several days. This quantity will serve for 10-15 students. For individual experiments, take one-tenth of the above amounts. b. Fit to the bottle a 1-hole stopper, L-tube, and rubber tube, terminating in a straight glass tube. Take 15 c.c. of limewater in a test-tube, insert the glass tube to the bottom of this, and shake the fermented liquid round in the bottle (?). Note the gas evolved and its reaction with limewater (?). In what form of solution was the gas before shaking? c. Filter off 100 c.c. of the fermented liquid, place it in a flask and distil as in Fig. 17, Exercise 17 b. After 30 c.c. has come over, empty and wash the flask, and re-distil the distillate until 6-8 c.c has come over. Note the odor o"? the distillate (?). Test it with litmus papers (?). Saturate a tuft of asbestos wool with the liquid, set the tuft on the base of the stand, and apply a light (?). Hold a cold, wide-mouth bottle over the flame, to recognize one l)roduct (?). Close the bottle and test the gas in the bottle by shaking with limewater (?). Make the equation for the combus- * You will certainly be disappointed if you attempt to reproduce this experi- ment on a large scale at home. The product obtained will not be satisfactory, and your friends will lose all confidence in your ability as a chemist. Better keep within the law, and confine your studies on CaHjOH to the laboratory. FERMENTATION 117 tion (?). If you burned alcohol vapor and pure oxygen, what rela- tive volumes should you use, and what relative volumes of the products (measured as gases) would be formed? d. Summarize the observed physical and chemical properties of alcohol (?). e. (Optional.) To a few drops of alcohol in a test-tube add 1 c.c. of sodium hydroxide solution. Pulverize one or two (not more) crystals of iodine, add a part of the powder to the mixture, shake vigorously, and warm (?). The amount added must not be sufficient to give a permanent brown tint to the liquid. The precipitate is iodoform CHI3 [449]. EXERCISE 60 Acetic Acid Object: To observe the properties of acetic acid, the difference between a strong and a weak acid, and the liberation of acetic acid from an acetate. Apparatus : Test-tubes. Materials: Acetic acid (6 A^). Sulphuric acid (dil.). Zinc (dust). Sodium acetate. Litmus papers. Litharge. a. Take 5 c.c. of acetic acid and note its odor (?). Test it with litmus papers (?). To the acid add 3-4 g. of litharge [618] and boil gently for a few minutes (?). Filter, if necessary, while hot, and set the clear solution aside to crj^stallize (?). What is thb common name of the product [619]? To show that acetic acid is a weak acid [274], take 15 c.c. of water in each of two test-tubes. To one add the 5 c.c. of acetic acid and to the other add an equal volume (5 c.c.) of dilute sul- phuric acid. Add a little zinc dust to the contents of each tube, and compare (?). Which reaction goes faster? If acetic acid had been added to the starch (Exercise 56 a) or sucrose (Exercise 56 d), instead of hydrochloric acid (a very active acid), what change in the procedure would have been necessary to get the same result? c b. To about 0.5 c.c. of sodium acetate add 2 c.c. of water and 1 c.c. of concentrated sulphuric acid. Warm and note the odor (?). Test the vapor with litmus papers (?). Make the equation, assuming that the second product is NaHS04 (?). c. Summarize the properties of acetic acid (?). How would you proceed to test for an acetate? 118 EXERCISE 61 Destructive Distillation of Wood and Coal Object: To study the products obtained by distilling wood and coal, such a» charcoal, coke, illuminating gas, etc. Apparatus: Test-tube (hard glass), tubing, large test-tubes and beaker. Glass rod. Materials: Sawdust and wood chips. Litmus papers. Bituminous coal (crushed). Lead nitrate (sol.). Filter-paper. a. Wood. Take three-fourths of a hard glass test-tube full of sawdust and wood chips. Arrange the apparatus as in Fig. 27. The test-tube is inclined slightly downwards towards the mouth. The wide test-tube, in which the distillate is to be caught, is surrounded by cold water, and a nozzle is inserted in one of the holes in the stopper. Heat the contents of the test-tube, at first gently, and later strongly, until no more vapors are evolved. During the heating, set fire to the issuing gas (?). Is the flame luminous, or not? Compounds of what ele- ment must be present? b. Examine the condensed liquid. What liquid or liquids are seen? Test the Hquid with litmus papers (?). What dissolved sub- stance causes this reaction [486]? Examine, describe, and name the residue in the hard glass test-tube (?). Place it in a corked test- ^^^- ^''• tube for use in Exercise 62. Name five observed products from distilling wood (?). c. Coal. Charge a hard glass test-tube with crushed soft coal, attach a clean test-tube to catch the distillate, and repeat a and b. 119 =-) 120 DESTRUCTIVE DISTILLATION OF WOOD AND C(JAL To test for hydrogen sulphide in the coal gas, dip a glass rod in lead nitrate solution, wipe it on a small piece of filter-paper, and hold the latter in the unlighted gas (?). What compound is formed on the paper [Exercise 39 d]? EXERCISE 62 Wood Charcoal and Bone Black Object: To study the properties of wood charcoal and of bone black. Apparatus: Iron wire. Test-tubes. Crucible (porcelain). Materials: Charcoal (splinters). Splints. Litmus (sol.). Wood charcoal (powdered;. Bone black. Molasses. Cupric sulphate (sol.). a. Charcoal. Hold first a splinter of wood and then a spHnter of charcoal in the flame (?). Describe how each burns (?). What is the cause of the flame in one case (?), and of the absence of flame in the other (?)? b. Place a splinter of charcoal in a test-tube half -filled with water. Is charcoal heavier or lighter than water? Hold the splinter of charcoal under the water by means of an iron wire, one end of which is twisted round it, and boil the water for five minutes. Remove the wire from the splinter. Does the latter now sink or float? le carbon specifically fighter or heavier than water? Why is fresh charcoal lighter [433]? c. To a test-tube half full of water add two or three drops of litmus solution. Add about 4 c.c. of powdered charcoal, boil for five minutes, and filter. Where is the litmus? What classes of sub- stances, especially, are readily adsorbed by charcoal [487-8]? d. Bone Black. Heat about 15 c.c. of bone black [504] in the cnicible (covered). The purpose of the heating is to make the charcoal more active by driving out gases and moisture already adsorbed on the surfaces of its pores. Take two test-tubes half filled with water, and add to one enough molasses to confer a dis- tinct tint, and to the other a few drops of cupric sulphate solution. Reserv^e a small portion of each for comparison with your final filtrates. When the bone black has cooled, put about 4 c.c. of it into each of your colored solutions, and shake vigorously. Filter the dilute molasses. If the filtrate is still colored (?), 121 122 WOOD CHARCOAL AND BONE BLACK pour it through the filter again. Taste the filtrate (?). Filter the dilute cupric sulphate, and examine the filtrate (?). What difference do you observe? Was the sugar removed, or only the coloring matter? Explain (?). What commercial use is made of this property of bone black [468]? EXERCISE 63 Tests for Food Components Object: To learn some tests for starch, glucose, milk-sugar, proteins, and fats. Incidentally, to show that starch is partly digested by saliva during mastication. Apparatus: Test-tubes. Evaporating dish. Materials: Starch. Iodine (sol. in KI). Glucose (solid). Fehling's solution (see Exercise 54). Alilk-sugar. Egg albumen. Nitric acid (cone). Am- monium hydroxide. Woolen yam. Fat. Cottonseed oil. Almonds (crushed). a. Starch. Place water in a test-tube, add a pinch of starch, shake, and boil (?). How does the starch change? Cool the suspension in running water, and when it is cold (not before), di\4de it into two parts and to one add a drop of the solution of iodine in potassium iodide (?). Keep the other half for use in d. b. Glucose. Shake about 0.5 c.c. of glucose in 5 c.c. of water. Add 5 c.c. of Fehling's solution and boil (?). c. Lactose (milk-sugar) : Repeat b with about 0.5 c.c. of milk- sugar (■?). d. Maltose from Starch. To 5 c.c. of the starch suspension prepared in a (which itself gives no reaction with Fehhng's solu- tion, Exercise 54 a), add about 1 c.c. of saliva, mix, and set aside for fifteen minutes. Then add 5 c.c. of Fehhng's solution and boil (?). How was the maltose produced [495]? e. Protein. To a few particles of egg albumen, add a few drops of concentrated nitric acid (?). Add some water to wash oif the acid, and pour away the liquid, leaving the sohd residue. To the latter add a few drops of ammonium hydroxide (?) . Repeat with a scrap of woolen yarn (?). Account for the effect of nitric acid on the skin and nails (?). f. Fat. Place on small pieces of unglazed paper (1) a particle of fat, (2) a drop of cottonseed oil, and (3) part of a crushed almond; put them in the evaporating dish, and warm gently until the fat melts. Examine the papers (?). 123 EXERCISE 64 Food Components of Milk Object: To find the food components -present in milk. To explain curdling. To learn a test for a common preservative, formaldehyde. Apparatus: Evaporating dish. Test-tubes. Glass rod. Materials: Milk. Nitric acid (cone). Ammonium hydroxide. Acetic acid. Fehling's solution (see Exercise 56). Litmus papers. Iodine (sol. in KI). Formaldehyde (1% sol.). Sulphuric acid (cone). Ferric chloride (sol.). a. Heat 50 c.c. of milk to boiling in the evaporating dish. With a glass rod, fish out the skin which forms on the surface and transfer it to a test-tube. Apply to it the test in Exercise 61 e for protein (?). Name the substance [495]. To the milk add three or four drops of acetic acid and stir (?). How is this result to be classified? What sort of substances cause milk to curdle? What is the connection with ''sour milk"? Filter the acidified milk and test the residue on the filter for protein (?). b. To 5 c.c. of the filtrate add 5 c.c. of Fehling's solution, and boil (?). What is shown to be present (Exercise 63 c)? c. To 5 c.c. of the filtrate from a add iodine solution (?). For what food component is this a test? Is it present? d. Put a few drops of unboiled milk on a piece of unglazed paper and heat as in Exercise 63 f (?). Result? e. Which food components have you found in milk? f. Test for Formaldehyde in Milk. To 5 c.c. of milk in a test- tube add an equal volume of water, and, by means of a glass rod, one drop (not more) of formaldehyde solution and shake. Take 5 c.c. of concentrated sulphuric acid and add to it by a glass rod one drop of ferric chloride solution. Now hold the test-tulx^ of milk almost but not quite vertical, and pour the sulphuric acid in a continuous stream down the side of the tube so that it may go to the bottom and form a layer under the milk. What color appears where the liquids meet? Repeat with diluted milk free from formaldehyde (?). 124 EXERCISE 65 Food Components of Flour Object: To find the food components in wheat flour. Apparatus: Evaporating dish. Test-tubes. Beaker. Materials: Flour. Cheesecloth (squares). Thread. Iodine (sol. in KI). Fehling's solution (see Exercise 56), Nitric acid (cone). Ammonium hydroxide. a. Take about 10 c.c. of flour, make it into a dough with water, and then place it in a small piece of cheesecloth. Bring the corners together and with a thread tie the cloth so as to enclose the dough in a bag. Knead the bag in water in the evaporating dish so long as the liquid squeezed out appears to be more milky than that in the dish. Then pour the milky liquid into a beaker to settle. Open out the cloth and wash the contents in running water until the wash- water is no longer milky. b. Test portions of the residue in the cloth for starch (?), glu- cose (?), and protein (?), and record the results (?). c. Test a pinch of the dry flour for fat (?). d. Pour the water away from the sediment in the beaker (from a) and test portions of the solid for starch (?), glucose (?), and protein (?), and record the results (?). e. Summarize the food components found in flour (?). 125 EXERCISE 66 Esters. Soap Object: To learn the nature of fats {which are esters) by forming and decom- posing a simple ester. To make soap and observe its properties. Apparatus: Test-tubes. Evaporating dish. Glass rod. Trip scales. Materials: Sodium acetate. Alcohol (95%). Sulphuric acid (cone). Methyl acetate. Litmus papers. Fat or cottonseed oil. Sodium hydroxide. Hydrochloric acid (dil.). Sodium hydroxide (sat. sol.). Sodium chloride (sol.). a. Formation of an Ester. To 1 c.c. of sodium acetate in a test-tube add 2 c.c. of alcohol and 1 c.c. of concentrated sul- phuric acid. Agitate for a minute or two, warm very slightly (do not boil!), and note the odor [451J (?). This is a test for acetic acid or an acetate. Write the equation (?), and name each substance (?). b. Hydrolysis of an Ester. Place 10 c.c. of water in one test- tube and 0.5 c.c. of methyl acetate CH3(C02CH3) in another. Test each with blue litmus paper (?), then mix and test again [498] (?). If the result is not definite, wait a few minutes and test the mixture once more. Write the equation (?), and name each substance (?). c. Saponification of an Ester: Soap Making. Alix in a test- tube 5 c.c. of cold, saturated sodium hydroxid(* solution and 5 c.c. of alcohol, shake, and allow to settle (?). Pour off the upper alco- holic layer into another test-tube, add to it an equal volume of fat or cottonseed oil, and shake (?). Put the liquid into an evaporating dish on the wire gauze and set fire to the contents. Warm the dish with a very small flame to assist in driving off the alcohol. Stir until the flame goes out, and then stop heating. The pasty mass is a soap, mainly sodium oleate and sodium palmitate [504], mixed with glycerine. Write an equation (?). Rub a little with water in the hands (?). 120 CfJCJ.CW 7V -—■-■■) ESTERS. SOAP 127 The alcohol is used simply as a common solvent for the fat and the alkali and is employed in the laboratory experiment to save time. d. Dissolve the soap (c) in a little warm distilled water and cool. To half of the solution in a test-tube add hydrochloric acid and shake vigorously [506] (?). To show that the precipitate is an acid, withdraw it by means of a glass rod, suspend it in 10 c.c. of water in another test-tube, add a few drops of sodium hydroxide solution and heat until solution takes place. Write the equation (?). To what class of substances does d show soap to belong? e. To the other half of the cold soap solution, add sodium chloride solution (?). This is called " salting out " [505]. To what class of solutions does this show soap solution to belong [508] ? EXERCISE 67 How Soap Cleanses Object: To obaerve the jjower of xo(ip Holutum to prrjduce an emulsion, and to clean a test-tube brush, covered with oil arui runt, aeparaiing the rust arul oil from orie aruAher as well as from thie brush. Apparatus: Test-tuJjes. Beaker (100 c.cj. Flask. Test-tube brush. Materials: Kerosene. Cottonseed oil. Ivory soap Csol. 1 : 10, hot). Sus- penf-ion of ferric oxide Cf>owderedj in cottonseed oil (fi g. in 100 c.c. for whole class J. a. Place 1 c.c. of kerosene in one test-tube and 1 c.c. of cotton- seed oil in another. Add ah)out 10 c.c. of water to each, shake vigorously and place in the rack (?). Is a permanent emulsion formed? Now add to each 2 c.c. of soap solution, shake again, and ol> serve as before (?). b. Boil 200 c.c. of water in a flask. Smear thoroughly the test-tube brush with the rust suspended in oil and push it into a test-tulxi. Add aVxjut 15 c.c. of the hot water, and work the brush in the tuVje (?). Does hot water alone remove the rust and oil? Itcniove the };rush, pour out the water, phico 15 c.c. of hot soap solution in the test-tube, and work the brush in the tulx; as before (?). Remove the brush, pour the contents of the test- tulxi into a 100 c.c. l>eaker, rinse first the brush and then the test- tube with hot water, catching the rinsing-water in the lx?aker. Have the oil and ru§j; been removed from the brush? After a short time, examine the contents of the beaker (?). Where is the oil (?) and in what condition? Where is the rust (?) and is it free from oil? Explain how soap solution removes grease or oil from a large object or a powder (?). 128 EXERCISE 68 Colloidal Suspensions Object: To prepare a colloidal suspension, and observe its properties. Apparatus: Test-tubes. Funnel. Square bottle (20-25 c.c). 300 c.c. beaker. Materials: Arsenic trioxide. Filter-paper. Hydrogen sulphide (sol.). So- dium chloride (sol.). Hydrochloric acid (cone). Calcium chloride (sol.). Sugar. Rosin. Alcohol (95% or denatured). Ferric chloride (sol. 5%). Sodium sulphate (sol.). Sodium carbonate (sol.). a. Preparation. Shake some arsenic trioxide with 25 c.c. of cold water vigorousl}^ for several minutes, filter, and to the filtrate add an equal volume of hydrogen sulphide solution. Arsenious sulphide AS2S3 is formed, but remains in colloidal suspension. b. Optical Examination. Pour the suspension into a square bottle, and examine it in sunlight, or, better still, by holding it close to an incandescent bulb. Look first through it towards the light (?). Does it appear to be transparent and clear, or not? Now look at it from a position at right angles to the direction of the light, and answer the same question (?). With an ultra- microscope, the particles in such solutions can be perceived, indi\ddually [506]. c. Coagulation. Di\dde the solution between 6 clean test- tubes. Keep one, corked, for reference and a second one for use in g. To the third add sodium chloride solution (?), to the fourth dilute hydrochloric acid (?), to the fifth calcium chloride solution (?), dissolve a little sugar in the sixth (?), and observe them from time to time. Note which coagulates last (?). The positive ion is here the coagulating agent. How does valence affect coagulating power? Do non-ionized, non-colloidal substances Uke sugar produce coagulation? After a day or two, does the arsenious sulphide in the reference test-tube coagulate or settle of its own accord? 129 130 COLLOIDAL SUSPENSIONS d. Colloidal Rosin. Dissolve a single particle of rosin in 1 c.c. of alcohol. Add the solution to a test-tube full of water (?). Ex- amine in the light as in b (?). Cork and keep, to see whether settling takes place (?). e. Summarize the special properties of colloidal suspensions (?). f. Colloidal Ferric Hydroxide. Boil 300 c.c. of distilled (or soft) water in a large beaker, and add to it, a few drops at a time, 3 c.c. of ferric chloride solution. The salt is thus hydrolyzed [541] to a significant degree, and contains suspended ferric hydroxide Fe(0H)3 (color?). Examine this suspension in the light as in b (?). Take 5 test-tubes full of the prepared liquid, keep one for refer- ence, and add to each of the others a very dilute solution of one of the following coagulants: sodium chloride, sodium sulphate, sodium carbonate, calcium chloride. This colloid is coagulated by the negative ion. Note the time required in each case (?). What is the effect of valence? g. To the reserved portion of your colloidal arsenious sulphide from c add successive small amounts of colloidal ferric hydroxide from f. What do you observe? What do you conclude as to the sign of the electrical charges on the two substances in colloidal suspension? EXERCISE 69 Dyeing. Dyes and Perfumes Object: To try two dyes, one of which dyes cotton directly , while the other will dye it only with the help of a mordant. To -prepare typical synthetic dyes and perfumes. Apparatus: Evaporating dish. Graduated cylinder. Test-tubes. Glass plate. Materials: White cotton cloth (pieces 5 by 2 cm.). White flannel (5 by 2 cm.). Hydrochloric acid (cone, and dil.). Ammonium hydroxide. Chrysophenin (suspension, 1%).* Sodium sulphate (sol., 8 g. Na2S04,- IOH2O per liter). Alizarin (suspended, 5 g. of 20% paste to 100 c.c. water). Aluminium sulphate (sol., A^). Phthalic anyhdride. Phenol. Resorcinol. Sulphuric acid (cone). Sodium hydroxide (dil.). Beta- naphthol. Methyl alcohol. a. Preparing the Cotton. In case the sizing has not been re- moved from the cotton cloth, boil three pieces in 50 c.c. of water containing 2 c.c. of concentrated hydrochloric acid. Rinse the goods in water, dip in 50 c.c. of cold water containing 0.5 c.c. of ammonium hj^droxide, and rinse again. b. Chrysophenin, a Direct Dye on Both Cotton and Wool. To 20 c.c. of water in the evaporating dish add 5 c.c. of the chryso- phenin suspension (shake the bottle) and 1 c.c. of sodium sulphate solution, and heat to boiling. Place in this bath one piece each of flannel and of cotton and keep them in motion with a glass rod for two minutes. Remove them and wash in running water (?). Is the dye fast to washing on both? What was the purpose of the sodium sulphate [515]? Smooth out the samples on a square of glass (or a bottle) to dry, and paste them in your note book. c. Alizarin, a Non-basic, Mordant Dye. In a test-tube dilute 2 c.c. of aluminium sulphate solution with 10 c.c. of water, place in it a piece of cotton cloth and boil for two minutes. In a second test-tube dilute 1 c.c. of ammonium hydroxide with * Congo-red or picric acid may be used instead of chrysophenin in this experiment, if desired. 131 132 DYEING. DYES AND PERFUMES 10 c.c. of water. Wring the piece of cloth, place it in this solu- tion and warm and shake for two minutes. Then wring the cloth, which is now mordanted with aluminium hydroxide. In the evaporating dish put 50 c.c. of water and 5 c.c. of the alizarin suspension (shake the bottle). Place in this the piece of mordanted cloth and a piece of unmordanted cotton, and heat to boiling. Keep the pieces of cloth in motion for at least ten min- utes. Finally, wash them in running water (?). Is the dye fast to washing on both? Why do they differ [513]? Dry the samples on glass and paste them into the note book. d. Preparation of Typical Dyes. Phenolphthalein. Take 0.1 gram of phthalic anhydride (the anhydride of phthalic acid, C6H4.(COOH)2) and 0.1 gram of phenol CeHs.OH in a test-tube, add two drops of concentrated sulphuric acid, and heat carefully for a minute over a small flame. The mixture, which should be well shaken during the heating, will turn dark-red in color. Allow to cool, add a few c.c. of water, and then add drop by drop a dilute solu- tion of sodium hydroxide until a pink color persists on shaking (?). Take a portion of this solution, and test the action of phenol- phthalein as an indicator by adding first dilute hydrochloric acid, then dilute sodium hydroxide [285]. e. Fluorescein. To 0.1 gram of phthalic anhydride and 0.1 gram of resorcinol C6H4(OH)2 add 3 drops of concentrated sul- phuric acid, and heat carefully for a minute. Allow to cool, add a few c.c. of water, then add sodium hydroxide until alkaline (use litmus paper as a test). Shake up a few drops of this solution with a test-tube of water. The dye imparts to the solution a brilliant green fluorescence, hence its name. f. Preparation of Typical Perfumes. Take 0.1 gram of beta- naphthol CioIIt.OII and 10 drops of methyl alcohol in a test-tube, add 2 drops of conc'fentrated sulphuric acid, and warm gently for a few minutes. The methyl ether of beta-naphthol, which is formed, has a most powerful odor, reminiscent of acacia blossoms. Repeat the experiment with ethyl alcohol instead of methyl alcohol. The ethyl ether of bota-naphthol is produced; its odor recalls the perfume of orange flowers. Cv EXERCISE 70 Recognition, of Substances I* Object: To learn how substances may he recognized by their properties, and to review the methods of preparation and properties studied in previous exercises. Apparatus : Test-tubes. Glass rod. Watch-glass. Materials: Unknowns. Litmus papers. Filter-paper. Sodium hydroxide (sol.). Limewater. Sulphuric acid (cone). Barium chloride (sol.). Hydrochloric acid (cone). a. Obtain [Instructor] a single unknown solid substance. This will contain one of the following radicals: ammonium (NH4) sulphite (SO3) chloride (CI) sulphate (SO4) carbonate (CO3) formate (CO2H) sulphide (S) base (OH) * Before you go on to Exercises 70 and 71, read carefully through pages 529-36 of the General Chemistry, and answer the questions on page 536 as far as possible without reference to preceding chapters. When you have finished, turn back to these chapters to ascertain how well (or how badly) j^ou made out on the questions. It is no use tr^'ing to identify a substance unless you know its distinctive properties. On the other hand, a perfect book know- ledge of properties will not be of much benefit to you, unless j'ou can make a successful analysis. Here is your opportunity to correlate your lecture and your laboratory work to a more intimate extent than has been possible in any way hitherto. See that you make the best use of it. The identification of imknowTis is exceedingly instructive, since it forces you to recall the more significant physical and chemical properties of practically all the important substances you have studied in the preceding weeks of the course. Keep your eyes open all the time, and remember that a negative result is often just as significant as a positive one. When you think you have discovered what your unknown is, always try to invent for yourself a con- firmatory test, utilizing the work done in previous experiments whenever possible. Do not guess, for you are almost certain to be wrong. Work sys- tematically and observe intelligently, and you will soon find that you can spot the unknown every time. 133 134 RECOGNITION OF SUBSTANCES I In the case of a salt (except one of ammonium) we shall limit ourselves to identifying the negative radical only. The other posi- tive radicals will, in any case, be limited to (Na), (K), and (Ca). Record at the time the result of each observation. Record negative results also. b. External Examination. Begin by recording the state (?), crystaUine form (?), color (?), and odor (?). c. Solubility and Reaction of Solution. Use a few particles to find out whether it is soluble in water (?). If in doubt, pro- ceed as in Exercise 22 a. Apply a drop of the solution to litmus papers (?). d. Efifect of Heating. Heat 0.5 c.c. in a dry test-tube. Watch the substance. Does it melt (?), char (?), or otherwise change (?)? Note also gases or vapors. If WATER VAPOR is given off and condenses (?), the substance may be a h^^drate, an organic substance, or calcium hydroxide. Incline the tube downwards, drive all the water off, dry out the tube with filter-paper, and continue heating. Does it now char (?), change (?), or give gases or vapors? If a SUBLIMATE (solid deposit in the tube) appears (?), it is a salt of ammonium. Note the odor (?) and apply the test (Exercise 46 e). A COLORLESS GAS with an odor (?) m.ay be ammonia, sulphur dioxide, or hydrogen sulphide, or gases from the charring of car- bohydrates (see e). A COLORLESS GAS with NO ODOR. Examine for carbon dioxide by inserting a rod dipped in limewater (?). If you get a positive result, what was the unknown substance? e. EflFect of Sulphuric Acid. To 0.5 c.c. of the substance add two or three drops (not more) of concentrated sulphuric acid (?). If necessary, warm gently (?). Watch the substance, and look out for gases. A COLORLESS GAS (bubbling), which fumes in the breath, is hydrogen chloride. If it does fume, what was the substance? A COLORLESS GAS which docs NOT FUME may have an odor (?). If the odor is that of hydrogen sulphide, what do you infer? If it is that of sulphur dioxide, inference (?). RECOGNITION OF SUBSTANCES I 135 A COLORLESS GAS, which does not fume and is odorless, may be carbon dioxide. Test with rod dipped in limewater (?). In- ference (?). It may be carbon monoxide. Try whether it is combustible (?). Inference (?). If there is no bubbling, there is no gas. The substance may be a sulphate. Test (Exercise 42 d) (?). It may be a base (test?). f. Report. State your conclusion, with the reasons therefor (?). g. Obtain a second unknown and proceed as before (?) EXERCISE 71 Recognition of Substances II Object: Same as in preceding exercise. Apparatus : Test-tubes. Glass rod. Watch-glass. Materials: Unknowns. Litmus papers. Filter-paj>er, Sodium hydroxide. Limewater. Splints. Ferrous sulphate (sol.). Sulphuric acid (cone). Potassium dichromate (sol.). Sulphuric acid (dil.). Ammonium molyb- date (sol.). a. Obtain [Instructor] a single unknown solid substance. This will contain one of the following radicals: peroxide (O2) phosphate (PO4) nitrate (NO3) bicarbonate (HCO3) chloride (CI) carbonate (CO3) bromide (Br) bisulphite (HSO3) iodide (I) sulphite (SO3) The positive radical may be (NH4), (K), (Na), or (Ca). Limit yourself to identifying the negative radical and (NH4). Record immediately the result of each observation. Record negative results also. b. External Examination. Record the state (?), crystalline form (?), color (?), and odor (?). c. Solubility and Reaction of the Solution. With a few i)ar- ticles, try the solubility in water and, if in doubt, use the method in Exercise 22 a (?). Test the solution on litmus papers (?). d. Effect of Heating. Heat 0.5 c.c. Does the substance melt (?), char, or otherwise change (?). Note also gases or vapors (?). If WATER VAPOR is givcu off (?), the substance may be a hydrate or an acid salt. To prevent cracking of the tube, remove the water with filter-paper. A SUBLIMATE indicates a salt of NH4 (test, E.xercise 46 e). A COLORLESS GAS with an odor (?) may be ammonia or sul- phur dioxide. Inference? 136 *, RECOGNITION OF SUBSTANCES II 137 A COLORLESS GAS with NO ODOR (?). Examine for carbon dioxide (lime-water test) oxygen from a peroxide or nitrate (test), or nitrous oxide (test, Exercise 49 c). Inference? e. Effect of Sulphuric Acid. To 0.5 c.c. add 2 or 3 drops (not more) of concentrated sulphuric acid (?). If necessary, warm gently (?). A GAS (bubbling) which fumes in the breath. If accompanied by a COLORED vapor, it may be hydrogen bromide with free bromine, or hydrogen iodide with free iodine. Nitric acid vapor, also, may be faintly colored with NO2 [411]. Inference? A GAS which FUMES, but is not colored, may be hydrogen chloride, or nitric acid (test, Exercise 47 c). Inference? A GAS (bubbling) may not fume and may not be colored. If it has an odor, it may be sulphur dioxide from a sulphite or bisulphite. The latter would give sulphur dioxide under d also, the former would not. Inference? A GAS, NOT fuming, NOT COLORED, and ODORLESS may be oxygen from some oxides or a peroxide (test. Exercise 35 d), or carbon di- oxide (test) from a carbonate or bicarbonate. The last would give carbon dioxide under d also, a soluble carbonate of K or Na would not, but calcium carbonate or ammonium carbonate would do so. Inference? If there is no gas (no bubbling), the substance may be a phos' phate (test. Exercise 50 b). Inference? f. Test the unknown for the (NH4) radical (Exercise 46 e). g. Report. State your conclusion, with the reasons therefor (?). h. Obtain a second unknown and proceed as before (?). I EXERCISE 72 ' Sodium Bicarbonate. Acid Salts Object: To prepare sodium bicarbonate by the Solvay process. To study the effect of heat on the bicarbonate and on another acid salt. Apparatus: Graduated cylinder. Test-tube (large) and cork. Trip scales. Gas generating bottle with thistle, L-, rubber, and glass delivery tubes. Test-tube, 1-hole stopper and L-tube. Test-tubes. Materials: Ammonium hydroxide (sol.). Ammonium carbonate. Sodium chloride. Marble (chips). Hydrochloric acid. Filter-paper. Lime- water. Sodium bisulphite. a. Preparation. Measure 24 c.c. of ammonium hydroxide solution and 12 c.c. of water into a large test-tube, add 8 g. of powdered ammonium carbonate, cork the tube and shake until the salt is dissolved. Add solid, powdered sodium chloride in excess and shake vigorously until the liquid is saturated. Decant the clear liquid into another test-tube, and lead into it carbon dioxide (made as in Exercise 53; be careful not to allow acid spray to be carried over (?)) until a copious precipitate (?) has appeared. While this is going on, proceed with b. Filter, and dry the precipitate by pressing between filter-papers. Note the appearance (?) and taste (?). Write ionic equations for the reactions involved. b. Effect of Heating the Bicarbonate. Place some sodium bicarbonate in a test-tube, fitted with 1-hole stopper and L-tube, so that the mouth is inclined slightly downwards, with the L-tube dipping into limewater. Warm the bicarbonate gently with a small flame. What ^as is given off? What is deposited in the cool part of the tube? Taste the residue when cold (?). To a part, add an acid (?). What is the residue? Write the equation for the action of heat on the bicarbonate? c. Effect of Heating Another Acid Salt. Many acid salts [328J Ix'have, when heated, as sodium bicarbonate did in b, and 138 SODIUM BICARBONATE. ACID SALTS 139 can be recognized by this behavior. Heat a little sodium bisul- phite in a test-tube, clamped horizontally (?). What gas (odor?) is given off? Is water Hberated? Write the equation (?). d. Summarize the properties of sodium bicarbonate and of sodium carbonate, namely, color (?), taste (?), effect of heating (?). e. (Optional.) Sodium Thiosulphate. Dissolve about 5 g. of sodium sulphite in about 20 c.c. of water in a small flask. Add 4-5 g. of flowers of sulphur to the solution and boil gently over a small flame for 10-15 minutes. Filter off the clear solution. To a portion of the filtrate add excess of any dilute mineral acid (?). Note the odor (?). Heat persistently about 1 g. of sodium thiosulphate in a porce- lain crucible over a blast-lamp (?). Note the appearance of the residue (?). When cold, add dilute hydrochloric acid (?) and identify the products. If any odor was observed during the heating, can you now account for it? EXERCISE 73 Potassium Nitrate Object: To prepare potassium nitrate, and to study the influence of solubility on the produ£ts obtained in double decomposition. Apparatus: Large test-tube. Trip scales. Beakers. Graduated cylinder. Glass rod. Watch-glass. Lens. Materials: Potassium chloride. Sodium nitrate. a. Dissolve 22 g. of potassium chloride in 45 c.c. of boiling water in a large test-tube (or small beaker). Boil 20 c.c. of water in a beaker (set on the wire gauze) and add 25 g. of sodium nitrate. When this has dissolved, add the boiling solution of potassium chloride and continue heating for a minute or so (?). Then allow the mixture to settle and immediately pour the hot liquid off the crystalline residue into another clean beaker. Examine the two products in b and c respectively. b. Pour a few c.c. of hot water on to the crystalline residue, stir with a rod to wash the residue and drain away the liquid. Taste the residue (?). Dissolve a part in a very little hot water, pour several drops on a watch-glass and examine the crystals, when they appear, with a lens (?). Draw two of them (?). What is the substance? c. When it is cold, examine the liquid that was poured off into the beaker in a (?). What form do most of the crystals show? Are there any cubical crystals (lens)? Pour away the liquid. Dissolve the crystals in a very little boiling water and set aside. Examine the final crystals and draw two of them (?). d. Write the equation for the action (?). Tabulate [184] the solubilities of potassium chloride, sodium nitrate, potassium ni- trate and sodium chloride at 20° and at 100° respectively. (Ex- trapolate to approximate values if necessary.) Which is the least soluble of the four salts at 20°, and which at 140 POTASSIUM NITRATE 141 100°? Why was sodium chloride the substance precipitated in the hot mixture? Why did potassium nitrate remain dissolved? Why did it come out so copiously when the liquid cooled? Why were there a few crystals of sodium chloride mixed with it? e. (Optional.) Potassium Hydroxide. Dissolve about 30 g. of potassium carbonate in 200-300 c.c. of water in a large beaker, and heat on a wire gauze to boiling. Slake 15-20 g. of quicklime in a beaker (?), using heat if necessary to start the action, and make the product into a very thin paste with water. Add this gradually, and with constant stirring, to the boiling solution (?). Continue boiling for a few minutes (why?). Let the mixture settle, and, when it is cold, decant the clear Hquid (or filter rapidly). Use the solution in b, c, and d. Is calcium hydroxide appreciably soluble [183-5]? Is calcium carbonate [180] more or less soluble than is the hydroxide? For- mulate the action and explain why it went to completion. What kind of hydroxides alone can be made by this method? Which hydroxides are of this kind [Inside front cover]? f. Place very small quantities of the following solutions in separate test-tubes, dilute with water, and add excess of the solu- tion of potassium hydroxide from e to each; ferric chloride (?); cupric sulphate (?); mercuric chloride (?). Describe the color and structure of the precipitates [199]. Boil the contents of each test-tube (?). Do the precipitates dissolve or change in any way? What kind of h3^droxides can be made by this method? Do any metals fail entirely to form hydroxides [544]? EXERCISE 74 Calcium Oxide and Hydroxide Object : To observe the formation of calcium oxide, and the actions of water and of an acid upon it. Apparatus: Wire gauze. 2 watch-glasses. Glass rod. Evaporating dish. Test-tubes. Materials: Marble (chips). Litmus paper (red). Quicklime (fresh). Hy- drochloric acid (dil.). a. Select two small chips of marble. Place one on the wire gauze and heat with the full flame for 10 minutes (meanwhile proceed with c and d). Examine it and compare its appear- ance with that of the unheated fragment (?). Write the equa- tion for the change (?). b. Place two strips of red litmus paper in two watch-glasses. Lay on one the heated fragment from a, and on the other the unheated fragment, and moisten each with water carried on a glass rod (?). What has been formed by the action of the water? Write the equation (?). What sort of oxide is calcium oxide [152]? c. Place a lump of quicklime in the evaporating dish, add a little water (only enough to wet the lower quarter of the lump) and warm gently (?). Write the equation (?). d. Place about 1 c.c. of powdered fresh quicklime in a test- tube, add dilute hydrochloric acid, shake, and warm if neces- sary (?). Write the equation (?). For comparison, take a chip of marble and cover it with dilute hydrochloric acid (?}^ Write the equation (?). What is the reason for the difference? e. Summarize the properties of marble and quicklime: color (?), apjx^arance (?), effect of heating (?), action of water (?), action of an acid (?). 142 EXERCISE 75 Hard Water Object: To learn the means of detecting hardness in water, and two ways of removing temporary hardness. Apparatus: Test-tubes. Gas generating apparatus. Graduated cylinder. Materials: Soap solution (12 g. per 1.). Limewater. Sodium carbonate (sol.). a. Soft Water. To about 10 c.c. of distilled water add soap solution drop by drop, shaking between drops. Count the num- ber of drops required before a '' permanent " lather or froth is obtained (?). A '^ permanent " froth is defined as one which persists for three minutes. b. Temporary Hardness. Take 5 c.c. of saturated limewater (1,7 g. Ca(0H)2 per liter) and add an equal volume of distiUed water. Pass carbon dioxide (made as in Exercise 53 a) through the half-saturated hmewater steadily until two changes (?) have occurred. Write two equations, one for each change (?). What substance is present in the final clear liquid? To 2 c.c. (measured) of this add soap solution (a few drops at a time) and shake until a " permanent " lather is obtained (?). The precipitate is a calcium soap. Write the formula of a typical com- ponent of this soap (?). Write the equation and name each sub- stance (?). c. To a second 2 c.c. (measured) of the clear product from b, add 1 c.c. (measured) of saturated limewater and shake (?). What is the precipitate [566]? Now add a few drops of soap solution, not- ing how much is required to form a '' permanent " lather? Was the amount required as great as in c, or was it nearer the amount used in a? d. Boil a third 2 c.c. (measured) of the clear product from b (?). What is the precipitate? When the Hquid is cold, add soap solu. tion as in c, to determine whether the hardness has changed (?). e. Test the city water with soap solution (?). 143 EXERCISE 76 Flame Tests for Metals Object: To observe the characteristic colors given to the Bunsen flame by the heated vapors of compounds of six metals, and to use them for recognizing six positive radicals. Apparatus: Test-tube. Iron wire (No. 20), or platinum wire. Cobalt glass. Materials: Chlorides of lithium, calcium, strontium, barium, sodium, and potassium. Hydrochloric acid (cone). a. On six pieces of paper write the names of the six salts hsted above and place on each a few particles of the proper substance. Provide 5 c.c. of concentrated hydrochloric acid in a test-tul)e. Hold the iron (or platinum) wire in the Bunsen flame. If the flame is colored by it, dip the wire in the acid, and hold it in the flame until the latter is as blue as usual. C'lean the wire in this way (i.e., by vaporizing impurities) before and after each of the following tests. b. Heat the tip of the cleaned wire and quickly touch the first named of the substances. Hold the wire with adhering particles in the lower part of the outer blue layer of the flame and note the color of the latter (?). Repeat with the next three substances, and tabulate the results, giving the name of the substance (?), its formula (?), and the color (?). c. Using sodium and potassiurrMihlorides separately in turn, view the flames given by each of these salts through a piece of cobalt glass. Which tint of light is absorbed by the glass, and does not reach the eye (?), and which tint passes through and is visible? Mix the two chlorides intimately, and observe the flame with the eye (?). Wliich color is visible? Why is the other invisible? Now view the flame of the mixture through cobalt glavss (?). (If you do not get good results with one piece of cobalt glass, try iivo thicknesses, one behind the other). Which metal can you recognize thus? d. Obtain an unknown and identify it. 144 EXERCISE 77 Compounds of Magnesium Object: To study the preparation of compounds by double decomposition, and (in d and e) to observe the properties of the carbonate and oxide of magnesium. Apparatus: Test-tubes. Glass rod. Materials: Magnesium chloride. Sodium hydroxide (sol.). Sodium car- bonate (sol.). Ammonium chloride (sol.). Ammonium hj^droxide (sol.). Sodium phosphate (sol.). Magnesium carbonate (powdered). Lime- Avater. Hydrochloric acid (dil.). a. Dissolve about 0.5 c.c. of magnesium chloride (properties ?) in 10 c.c. of water, and divide the solution into three portions. To one portion add sodium hydroxide solution (?). Remember that salts, bases, and acids usually interact by double decomposi- tion. On this basis, write the equation (?), and name each sub- stance (?). b. To the second portion add sodium carbonate solution (?). Why does the addition of sodium bicarbonate to table salt con- taining magnesium chloride prevent the salt from becoming moist in damp weather? c. Test. To the third portion add ammonium chloride solution (not included in equation), then a little ammonium hydroxide solution (?), and finally a little sodium phosphate solution (?). Rub the inside of the test-tube with a glass rod and note where the precipitate appears (?). d. Heat 0.5 c.c. of powdered magnesium carbonate in a test- tube and lower into the gas a rod dipped in limewater (?). Write the equation (?). Use the residue — after strong heating — in e. e. To the residue from d, when cold, add water (?). Take a little of the moist paste from the tube, and try its effect on red and on blue Htmus papers (?). To the residue in the tube add dilute hydrochloric acid (?). What sort of oxide is magnesium oxide? 145 EXERCISE 78 Aluminium Hydroxide. Alum Object: 7 o [fTK^/^irti a dfr>Me unit in bea^itipd cryidaU. To rAjfterte the forrruitifm of aluminium hydroxi/ie, and iU jrrr/jjertien. Apparatus: T*iflt-tufj'.staLs. What is their formula [581]? b. Alamininm Hydroxide. Dilute 2 c.c. of aluminium sul- phate solution with 20 c.c. of water. Test the reaction of the solution with litmas papers (?). Explain. To one half of the .solution add sodium hydroxide, drop by drop, noting carefully what rxrcurs, (I) when a small amount is added, (2) when excess is added. Write equations for the two reactions *hat occur. WTiat kind of an electrol>i:e is aluminium hydroxide? To the other half of the soltrtion add ammonium hydroxide, procef'ding just as before {?). What difference is there in the Uiha^ior of the two bases towards aluminium hydroxide? To whiat may this difference \xi ascriU^d [274j? Would you expect ammonium aluminate to be stable in aqueous solution [642]? c- CoagolatioiL Take 100 c.c. of water with clay in suspen- sion, add 1 c.c. of aluminium sulphate solution, stir vigorously, and then add 15 c.c. of lime water. Observe the water after it has stooi^i for .some time (?). Explain [581] (?). 140 EXERCISE 79 Analysis of Baking Powder Object: Baking poioders contain (/) sodium bicarbonate, (2) a substance which is acid (or becomes so on being heated), and (5) starch to delay interaction. The acid (or acid-forming) substance may be potassium bitartrate KHC4H4O6, or calcium acid phosphate Ca(H2P04)2, or potassium bisidphate KHSO4, or ammonium alum (NH4)2S04,Al2(S04)3,24H20. The object is to learn tests for the presence of the radicals of these substances. Apparatus: Test-tubes. Funnel. Evaporating dish. Platinum wire. Materials: Baking powder. Filter-paper. Sulphuric acid (cone). Nitric acid (dil.). Ammonium molybdate (sol., Exercise 50). Hydrochloric acid (dil.). Barium chloride (sol.). Sodium hydroxide (sol.). Litmus papers. Ammonium hydroxide (sol,). Acetic acid (dil., 6 N). Am- monium oxalate (sol.). Iodine (sol. in KI). Cobalt chloride (sol.). a. Preparatory. Place about 4 c.c. of the baking powder in a large test-tube, add 20 c.c. of water, and shake vigorously for several minutes. Test the gas that is given off by means of a glass rod dipped in limewater. Filter the liquid and test the clear filtrate as in c, d, e, and f . b. Starch (see Exercise 56 b). Perforate the filter-paper and with water wash some of the residue into a test-tube. Boil this suspension, and then cool it and fill the test-tube up with water. With a glass rod, add to the suspension one drop of the iodine solution (?). A blue color indicates starch. c. Tartrate Radical. Place 4 c.c. of the filtrate (a) in an evapor- ating dish with 5 drops of concentrated sulphuric acid and evap- orate to dryness over a small flame. Charring and an odor of burnt sugar indicate a tartrate. d. Phosphate Radical (see Exercise 50 b). Take 1 c.c. of the filtrate (a) and acidify with 1 c.c. of dilute nitric acid. To 5 c.c. of ammonium molybdate solution add 3 drops of this mixture, warm, and set in the rack (?). Phosphates give a yellow pre- cipitate. 147 148 ANALYSIS OF BAKING POWDER e. Sulphate Radical (see Exercise 42 d;. Acidify about 5 c.c. of the filtrate (a) with 5 c.c. of dilute hydrochloric acid and add barium chloride .solution (?). What i.s the precipitate (if any)? f. Ammonium Radical (Exercise 46 e). To 5 c.c. of the filtrate (a) add 5 c.c. of sodium hydroxide solution. Heat to boihng and note the odor (?) and reaction of the vapor (not the liquid) towards moLst red Htmas paper (?). What is the gas (if any)? g. Calcium Radical. Shake about 0.5 c.c. of the baking powder with 5 c.c. of dilute hydrochloric acid. Filter and to the filtrate add ammonium hydroxide until the liquid is alkaline to htmus. Now add acetic acid until the solution is acid to litmus, boil, and filter if the liquid is not clear. Add ammonium oxalate solution. The precipitate, if any, is calcium oxalate [451]. h. Aluminium Radical. Wrap a few particles of the powder tightly in a small piece of filter-paper, and wind the platinum wire spirally round the mass. Char the little ball in the Buasen flame, moisten it with cobalt chloride solution, applied with a glass rod, and heat again (?). The blue color of the avsh is char- acteristic of aluminium. ' j. Report. Summarize, stating which radicals were present and which absent (?). \ EXERCISE 80 Reactioxs of Irox Compouxds Object: To try the tests for ferrous and ferric salts, and to learn how ferrous salts are changed into ferric salts and vice versa. Apparatus: Test-tubes. 1-hole stopper. L- and deliverj' tubes. Funnel. Unsized paper, white sheets. Brush, camel's hair. Photographic print- ing frame. Stained cloth. Materials: Ferrous sulphate. Ferric chloride fsol.V Potassium ferro- cyanide fsol.^ ferricyanide ''cn-st. and sol.), and thiocyanate (sol.). Fer- rous cliloride (sol.). Chlorine-water. Ammonium hydroxide. Am- monium-ferric citrate. Ammonium oxalate. Ferrous sulphide. Hydro- chloric acid (dil.). Iron (powder). Filter-paper. a. Tests for Ferrous and Ferric Salts. Wash some crj'^als of ferrous sulphate in water until the surface layer has been removed by solution. ^\liy is this necessary-? Dissolve the clean crj'stals in 15 c.c. of distilled water and di^^de into three parts. Dilute 5 c.c. of ferric chloride solution with 10 c.c. of water and di\'ide this also into three parts. Test each of the solutions with the three following reagents and tabtilate the results: Potassium Potassium Potassium Ferrocyaxide Ferricyaxide Thiocyaxate Ferrous : Ferric: In the table, note the color produced (?), and whether there is a precipitate or simply a colored solution (?). Repeat the tests with xevy highly diluted solutions, so as to form an estimate of their relative sensiti\'ity. Include this in your tabulation. Write the equations for all the interactions [611] (?). Potassium thiocyanate is K(CXS). Give one distinctive test for a ferrous salt (?) and two for a ferric salt(?). b. Oxidation of Ferrous Compounds. To a solution of fer- rous chloride add an oxidizing agent [316] such as chlorine-water, 149 150 REACTIONS OF IRON COMPOUNDS hydrogen peroxide (acidified), or bromine-water. Then test for ferric-ion, using tests from a. What change has the ferrous-ion undergone? c. Boil some water in a test-tube to remove dissolved oxygen, and cool in running water. Wash off the surface layer from a crystal of ferrous sulphate, and dissolve the clean crystal in the boiled water. Now add a few drops of ammonium hydroxide (?). Shake the mixture with air, and note any changes (?). Give the name and the formula of the first precipitate (?) and of the final product (?). d. Reduction of a Ferric Compound. Dilute some ferric chlo- ride solution. Through half of it bubble some hydrogen sulphide, made (Exercise 39 a) in a test-tube provided with a 1-hole stopper and delivery tube (?) . Test small portions until the liquid no longer gives the reactions for a ferric salt. The precipitate is sulphur. What change has the ferric-ion undergone? Boil the other half of the ferric chloride solution with iron powder for several minutes, filter, and test quickly for ferrous- ion (?). Write the equation. e. Blue-prints. Dissolve 10 g. of potassium ferricyanide in 100 c.c. of water, and 13 g. of ammonium-ferric citrate in a second 100 c.c. Mix equal volumes of the two solutions and filter if there is any precipitate. Paint evenly over unsized paper with a clean camel's hair brush, dry, and keep in a dark place until required. When dry the paper is sensitive to light. Expose a sheet to bright sunlight in a photograplric printing-frame. Wash thor- oughly in very dilute hydrochloric acid. Why is the paper blue? Repeat with a second sheet, placing a fern or a design cut out of paper, or a photographic negative, in front of the paper. Why is the protected part utlchangod in color? f. Removal of Ink and Rust Stains. Stains of fresh writing ink (ferrous tannate, colorless, and an organic dye; both soluble) can usually be washed out with water, if the latter is used at once. After the oxidation has occurred, the ferric tannate (black, insoluble) must be reduced again, by soaking the cloth for 12 hours or longer in ammonium oxalate solution, before the stain can be REACTIONS OF IRON COMPOUNDS 151 washed out. Rust stains are often rendered soluble by ammonium oxalate also. Take a piece of white linen, stamed with ink or rust, and treat with ammonium oxalate solution as above. Interpret the result. fSkrMMAnom of Lxad, yiEmccmr axd SiL.rBB ju Laul CUmku Dilnfe 2 ex. of kad ii 5 ex. of water and add dilate hfdmdakne i ribakiiig Ixtiimi dns^ and aflonrnig tibe pvi^' to settle^ until tbe next drop prodiie» no In lu Wben iht pie^Mtate has aeiticd, por. wiiat do» llw cootaiii?). Shake the preei; risrtilkd water^ and aDoir it to settle, and liqnid. y^^m hoSk Ihe pieeqiitate witb Ss^tilk c Dinde tiie aolntiaD into two part^ Set obnennstiiMi (?). To llie otlier add polmiiiiiiii (% WmfAmMjoaie€OffdMa9Mtilewaitir 4L liewww Cliariifc. Bf^ttsmi a and h, . nitnite soiotioii (?>. I>des the pnaptu Add to the mtpended predpitate aome affi ^?>, How ffivypsM r^ feesjpuje a acMMe mer cu fllHvr CUoride. Bepcat a and b, ort . initiate aolntictt (T>. Dbn the precipitate ri Diiride Ihe mmfeadid precipitate Imto tw , ID the rtnni^at 1%^ amIaUe and examiDe it btrf fwf. M. ute. ^ •'VtM^. i-U4Wvr. iifA. rrttnm^nml '.>A\u*fiA'.. APPENDIX 169 Phosphorus, red. PhthaUc anhydride. Potassium bitartrate. bromide. chlorate. choride. chromate. dichromate. ferri cyanide. fcrr()(!yanide. hydroxide. iodide. permanganate. sodium tartrate (Rochelle Salt). sulphate. thiocyanate. Resorcinol. Rosin (powdered). Rubber bands (small). Sand. Silver nitrate. Soap, castile. ivory. Soda-lime. Sodium acetate. bicarbonate. bisulphate, commercial. bisulphite. carbonate (anhyd). Sodium carbonate (cryst.). chloride. hydroxide. nitrate. peroxide. phosphate. sulphate (cryst.). Stannic oxide. Stannous chloride. Starch. Strontium chloride. Sugar, milk. Sugar, ordinary (sucrose). Sulphur, flowers. roll. Tin, foil (lead-free). granulated. Toluene. Vinegar (white). Wood, sawdust and chips. Wood, splints (tobacconists'). Woolen yarn. Yeast. Zinc, dust. granulated. sReet. Zinc oxide. sulphate.